GEO CHAPTER 2 - MIDTERMS PDF

CHAPTER 2: MINERALOGY 78 | P a g e LESSON 1: ELEMENTARY KNOWLEDGE ON SYMMETRY OF CRYSTALLOGRAPHIC SYSTEMS The minerals that make up igneous rocks crystallize at a range of different temperatures. This explains why a cooling magma can have some crystals within it and yet rema...

CHAPTER 2: MINERALOGY 78 | P a g e LESSON 1: ELEMENTARY KNOWLEDGE ON SYMMETRY OF CRYSTALLOGRAPHIC SYSTEMS The minerals that make up igneous rocks crystallize at a range of different temperatures. This explains why a cooling magma can have some crystals within it and yet remain predominantly liquid. The sequence in which minerals crystallize from a magma is known as the Bowen reaction series. Of the common silicate minerals, olivine normally crystallizes first, at between 1200° and 1300°C. As the temperature drops, and assuming that some silica remains in the magma, the olivine crystals react with some of the silica in the magma to form pyroxene. As long as there is silica remaining and the rate of cooling is slow, this process continues down the discontinuous branch: olivine to pyroxene, pyroxene to amphibole, and amphibole to biotite. At about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize. At that temperature, the plagioclase is calcium-rich (anorthite). As the temperature drops, and providing that there is sodium left in the magma, the plagioclase that forms is a more sodium-rich variety. WHO WAS BOWEN, AND WHAT’S A REACTION SERIES? Norman Levi Bowen, born in Kingston Ontario, studied geology at Queen’s University and then at MIT in Boston. In 1912, he joined the Carnegie Institution in Washington, D.C., where he carried out groundbreaking experimental research into the processes of cooling magmas. Working mostly with basaltic magmas, he determined the order of crystallization 79 | P a g e  of minerals as the temperature drops. The method, in brief, was to melt the rock to a magma in a specially made kiln, allow it to cool slowly to a specific temperature, and then quench it so that no new minerals form. The results were studied under the microscope and by chemical analysis. This was done over and over, each time allowing the magma to cool to a lower temperature before quenching. The Bowen reaction series is one of the results of his work, and even a century later, it is an important basis for our understanding of igneous rocks. The word reactionis critical. In the discontinuous branch, olivine is typically the first mineral to form (at just below 1300°C). As the temperature continues to drop, olivine becomes unstable while pyroxene becomes stable. The early-forming olivine crystals react with silica in the remaining liquid magma and are converted into pyroxene, something like this: Mg2SiO4 + SiO2 ——> 2MgSiO3 olivine pyroxene In cases where cooling happens relatively quickly, individual plagioclase crystals can be zoned from calcium-rich in the centre to more sodium-rich around the outside. This occurs when calcium-rich early-forming plagioclase crystals become coated with progressively more sodium-rich plagioclase as the magma cools. Shows a zoned plagioclase under a microscope. A zoned plagioclase crystal. The central part is calcium-rich and the outside part is sodium-rich Finally, if the magma is quite silica-rich to begin with, there will still be some left at around 750° to 800°C, and from this last magma, potassium feldspar, quartz, and maybe muscovite mica will form. The composition of the original magma is critical to magma crystallization because it determines how far the reaction process can continue before all of the silica is used up. The compositions of typical mafic, intermediate, and felsicmagmas are shown in Figure 3.12. Note that, unlike, these compositions are expressed in terms of “oxides” (e.g., Al 2O3 rather than just Al). There are two reasons for this: one is that in the early analytical procedures, the results were always expressed that way, and the other is that all of these elements combine readily with oxygen to form oxides. 80 | P a g e The chemical compositions of typical mafic, intermediate, and felsic magmas and the types of rocks that form from them. Mafic magmas have 45% to 55% SiO2, about 25% total of FeO and MgO plus CaO, and about 5% Na2O + K2O. Felsic magmas, on the other hand, have much more SiO2 (65% to 75%) and Na2O + K2O (around 10%) and much less FeO and MgO plus CaO (about 5%). QUESTIONS: 1. Which minerals are the first to crystallize from cooling magma? 2. Which minerals are most common in granite? 3. How long does it take for magma to cool underground? 4. Which minerals crystallize at high temperatures? 5. How are minerals formed by crystallization from magma? 81 | P a g e LESSON 2: PHYSICAL PROPERTIES OF MINERALS Rocks are composed of minerals. A mineral is a naturally occurring substance which is usually solid, crystalline, stable at room temperature and inorganic. There are almost 5000 known mineral species, yet the vast majority of rocks are formed from combinations of a few common minerals, referred to as “rock-forming minerals”. The rock-forming minerals are: feldspars, quartz, amphiboles, micas, olivine, garnet, calcite, pyroxenes. Minerals occurring within a rock in small quantities are referred to as “accessory minerals”. Although accessory minerals are present in only small amounts, they may provide valuable insight into the geological history of a rock, and are often used to ascertain the age of a rock. Common accessory minerals are: zircon, monazite, apatite, titanite, tourmaline, pyrite and other opaques. The abundance and diversity of minerals depend on the abundance in the Earth’s crust of the elements of which they are composed. Eight elements make up 98% of the Earth’s crust: oxygen, silicon, aluminium, iron, magnesium, calcium, sodium and potassium. The composition of minerals formed by igneous processes is directly controlled by the chemistry of the parent body. For example, a magma rich in iron and magnesium will form minerals such as olivine and pyroxene (as found in basalt). Magma richer in silicon will form more silica-rich minerals such as feldspar and quartz (as found in granite). It is unlikely that a mineral will be found in a rock with dissimilar bulk chemistry unlike its own; thus, it is unlikely that andalusite (Al2SiO5) would be found in an aluminium-poor rock such as a quartzite.  PHYSICAL PROPERTIES OF MINERALS Some minerals are easily identifiable; others can only be recognized only by the use of a petrographic microscope or by complex analytical techniques. The following criteria are used to differentiate minerals in hand sample. Most minerals cannot be identified from one particular property, and so it is advisable to use several of the diagnostic criteria outlined below. A hand lens will assist you greatly.  COLOUR It is one of the most obvious characteristics of a mineral, but generally not the most useful diagnostic feature. Depending on impurities, individual mineral types may come in a vast variety of colours. For example, ruby and sapphire are differently coloured types of the mineral corundum (Al2O3). The red colour of ruby is due to the presence of the element chromium. Sapphires may come is a vast variety of colours; blue is the most familiar colour, but yellow, orange, green, pink, orange and brown varieties are also known. 82 | P a g e Garnets may also come in a large range of colours, depending on their composition. They can be found with virtually any colour, although blue garnets are exceptionally rare. It is therefore advisable not to rely on colour alone to identify a mineral.  CRYSTAL HABIT It refers to the characteristic shape of a mineral unit (either an individual crystal or an aggregate of crystals). Crystals with well-developed faces are referred to as “euhedral”; for example, garnet crystals are often euhedral. Minerals may also occur as aggregates of crystals; for example, asbestos is usually found as an aggregate of very fine fibres. The following list gives examples of different crystal habits and examples of common minerals that may exhibit each habit. Acicular – needle-like, e.g. natrolite, Granular – aggregates of crystal, e.g. rutile bornite, scheelite Bladed – blade-like, slender and Hexagonal -six-sided, e.g. quartz, flattened, e.g. kyanite hanksite Botryoidal – grape-like masses, e.g. Massive – no distinct shape, e.g. hematite, malachite turquoise, realgar Columnar – long, slender prisms, e.g. Octahedral – eight-sided, e.g. diamond, calcite, gypsum magnetite Cubic – cube-shaped, e.g. pyrite, Platy – flat, tablet shape, e.g. wulfenite galena, halite Dendritic – tree-like, branching in Prismatic – elongate, prism like, e.g. multiple directions, e.g. pyrolusite, tourmaline, beryl native copper, native silver Radial or Stellate – radiating outwards Fibrous – very slender prisms, e.g. from a central point, star-like, e.g. asbestos, tremolite wavellite, pyrophyllite Foliated or Lamellar – layered structure, parts easily into very thin sheets, e.g. muscovite, biotite Acicular Habit (Rutile) Botryoidal Habit (Malachite) Cubic Habit (Pyrite) 83 | P a g e  Fibrous Habit (Silimanite) Foliated Habit (Biotite) Hexagonal Habit (Sapphire) Massive Habit (Realgar) Platy Habit (Wulfenite) Prismatic Habit  HARDNESS Hardness is a measure of how resistant a mineral is to scratching. This physical property is controlled by the chemical composition and structure of the mineral. Hardness is commonly measured on the Mohs scale. This is defined by ten minerals, where each mineral can scratch those with a lower scale number. Diamond (hardness 10) can scratch everything below it on the Mohs scale, but cannot itself be scratched, whereas quartz (hardness 5) can scratch calcite (hardness 3) but not corundum (hardness 9). SCALE NUMBER INDICATOR MINERAL COMMON OBJECTS 1 Talc 2 Gypsum Fingernail 3 Calcite Copper Coin 4 Fluorite 5 Apatite Knife Blade 6 Orthoclase Window Glass 7 Quartz Steel File 8 Topaz 9 Corundum 10 Diamond 84 | P a g e   STREAK The streak of a mineral refers to the colour of the mark it leaves behind after being rubbed against a piece of unglazed porcelain. Hematite provides a good example of how streak works. While this mineral is usually black, silver or brown-red in hand sample, its streak is always a dark blood-red. Chalcopyrite is usually golden-brown in hand sample, but has green-black streak. Streak can be used only for minerals with a Mohs hardness of 7 or less, as minerals with a hardness greater than 7 will themselves scratch the streak plate.  LUSTRE Lustre refers to the way in which the surface of a mineral reflects light, and is controlled by the kinds of atoms present and their bonding. It is described by the following terms:  Adamantine – diamond-like lustre; such minerals are usually transparent and have a high refractive index; e.g. diamond, cerussite, cubic zirconia  Dull or Earthy – no reflections; e.g. kaolinite  Greasy – the appearance of being coated with an oily substance; may also be greasy to the touch; e.g. opal  Pearly – the whitish iridescence of materials such as pearls; e.g. stilbite  Vitreous – like glass; e.g. calcite, quartz, beryl  Silky – like silk fabric; e.g. satin spar (a variety of gypsum)  Resinous – like a resin; e.g. fire opal  Metallic – metal-like in appearance; e.g. pyrite Adamantine Lustre (Diamond) Resinous Lustre (Fire Opal)  CLEAVAGE Minerals are composed of atoms, which, for each mineral, have a characteristic arrangement. Weaknesses in the chemical bonds between these atoms cause planes of weakness in the crystal structure. Cleavage is an indication of how well a mineral break along these planes of weakness, and may be a good diagnostic characteristic. Cleavage may be described as “perfect”, “good”, “distinct” or “poor”. In transparent minerals or in thin sections viewed though a microscope, cleavage may be seen as a series of parallel lines. 85 | P a g e  The number of cleavage planes in a mineral may also aid its identification. Cleavage typically occurs in either one, two, three, four or six directions. Micas easily split along their one plane of cleavage to form thin sheets. Amphiboles exhibit two cleavage planes. Iceland spar, a variety of calcite, cleaves readily along three planes of weakness into distinctive rhombs. Galena breaks along three cleavage planes producing cubic fractions. Fluorite and diamond show cleavage in four directions. Sphalerite exhibits cleavage in six directions. Not every mineral display cleavage. For example, quartz does not have weakness in its crystal structure, and therefore does not exhibits cleavage. When a quartz specimen is broken with a hammer, it displays conchoidal (shell-like) fracture. Calcite has three cleavage planes.  QUARTZ Quartz is one of the most well-known minerals on earth. It occurs in basically all mineral environments, and is the important constituent of many rocks. Quartz is also the most varied of all minerals, occurring in all different forms, habits, and colors. There are more variety names given to Quartz than any other mineral. Although the Feldspars as a group are more prevalent than Quartz, as an individual mineral Quartz is the most common mineral. Most mineral reference guides list Chalcedony as an individual mineral, but in reality it is a variety of Quartz. It is the microcrystalline form of Quartz, forming only occurs in microscopic, compacted crystals. This page deals only with the crystalline forms of Quartz. Chalcedony is listed on its own dedicated page in this guide. Other important varieties of Quartz, such as Amethyst, Citrine, and Agate, also have dedicated pages due to their popularity and individual varieties. Some forms of Quartz, especially the gemstone forms, have their color enhanced. Almost all forms of the yellow-brown variety Citrine are in fact heat treated. Much Amethyst is also heat treated to intensify color, and a green transparent form known as "Green Amethyst" or "Prasiolite" is formed by heat treating certain types of Amethyst. There is also a transparent sky blue form of Quartz crystals, as well as a wildly iridescent type that are synthetically colored by irradiation of gold. In some localities, Hematite forms a thin red or brown layer internally in the Quartz crystal, giving it a natural bright red to brown coloring, and sometimes even a mild natural iridescence. 86 | P a g e Quartz frequently forms the inner lining of geodes. Most geodes have an inner layer of larger crystalline Quartz, and an outer layer of Chalcedony or banded Agate. PHYSICAL PROPERTIES OF QUARTZ CHEMICAL SiO2 FORMULA COMPOSITION Silicon Dioxide Colorless, white, purple, pink, brown, and black. COLOR Also, gray, green orange, yellow, blue, and red. Sometimes multicolored or banded. STREAK White HARDNESS 7 CRYSTAL SYSTEM Hexagonal 3D CRYSTAL ATLAS CRYSTAL FORMS Crystals, which are hexagonal in shape, vary in AND AGGREGATES shape and size. Quartz crystals are unique and very identifiable with their pointed and often uneven terminations. Crystals can be in enormous prismatic and stubby crystals, or in pointed aggregates of such crystals. Crystals are usually striated horizontally, and are sometimes doubly terminated. Quartz crystal habits include drusy, grainy, bladed, as linings of geodes, as rounded waterworn pebbles, radiating, as pointy pyramids on a matrix, as dense agglomerations of small crystals, massive, globular, stalactitic, crusty, in nodules, and in amygdules. Crystals frequently twin; a famous twinning habit is the Japanese twin, where two crystals contact at a 90° angle. Quartz crystals may also contain a scepter growth, where the top of a crystal bulges out from the rest of the crystal, and may also from as phantom growth, where one crystal forms over another, leaving a ghosted form inside. The crystal structure of Quartz is very complicated. As a result of a changeover from alpha to beta Quartz, crystals form as hexagonal prisms with modified crystal faces. TRANSPARENCY Transparent to opaque SPECIFIC GRAVITY 2.6 – 2.7 87 | P a g e  Vitreous. Transparent, colorless Quartz crystals from LUSTER a few distinct localities may be adamantine. CLEAVAGE Indiscernible. Seldom exhibits parting. FRACTURE Conchoidal TENACITY Brittle OTHER ID MARKS 1) Some specimens fluoresce, especially white and green. 2) Triboluminescent. 3) Piezoelectric. COMPLEX TESTS Dissolves in hydrofluoric acid IN GROUP Silicates; Tectosilicates; Silica Group Hardness, crystal forms, striations on crystal faces, STRIKING and frequent appearance of conchoidal fractures on FEATURES crystal faces. Quartz occurs in almost every single mineral ENVIRONMENT environment. ROCK TYPE Igneous, Sedimentary, Metamorphic POPULARITY (1-4) 1 PREVALENCE (1-3) 1 DEMAND (1-3) 1 VARIETIES FOR AMETHYST, CITRINE, AND CHALCEDONY ARE LISTED SEPARATELY:  AMETHYST – purple variety of  AVENTURINE – opaque form of Quartz. compact Quartz or Chalcedony containing small Mica, Hematite, or Goethite scales which cause a glistening effect.  AQUA AURA  BLUE QUARTZ – quartz – Is a very uncommon synthetically in nature and rarely in enhanced with crystal form. Blue coating using gold quartz may also refer (and sometimes to a dull grayish-blue quartz in other metals) to give it a neon blue massive form with Crocidolite or other neon color. inclusions.  CACTUS QUARTZ – form of  CHALCEDO quartz, usually NY – Amethyst, Citrine, or microcrystalline a combination of the form of Quartz. two, that contains a large crystal or crystals overgrown with a layer of spiky smaller 88 | P a g e  crystals.  CITRINE –  FADEN yellow, orange, or QUARTZ – group of brown variety of quartz crystals with Quartz. a white thread-like zone running through the interior, with the crystals having formed around the thread axis.  FERRUGINOUS QUARTZ – quartz  HERKIMER with an opaque DIAMOND – red to brown exceptionally Hematite coating lustrous and clear to internal quartz crystals from inclusion. the Herkimer Co. vicinity in the Mohawk Valley region of Central New York State. Herkimer Diamond crystals are usually doubly terminated and short.  MILKY  MORION – QUARTZ – white, opaque form of black translucent to quartz. A type of opaque variety of Smoky Quartz. Quartz.  PHANTO  PRASE – M QUARTZ – light to emerald quartz green, transparent containing to translucent internal phantom Quartz, with growths, or coloring caused ghostlike layers within a crystal. from inclusions of green minerals, such as Actinolite, Hedenbergite, Chlorite, or Malachite.  PRASEME  PRASIOLITE – light green, – describes a light translucent form green quartz of Quartz with artificially colored Hedenbergite by heat treatment of inclusions found certain types of on Serifos Island, Amethyst. May also Greece. be called Green Amethyst by some jewelers. 89 | P a g e   RAINBOW QUARTZ – quartz  ROCK synthetically CRYSTAL – colored with an colorless, iridescent layer transparent variety formed from gold of quartz in large or other metals. crystal form. Also see Aqua Aura.  ROSE  RUTILATED QUARTZ – pink QUARTZ – quartz variety of Quartz. with golden yellow, needle-like Rutile inclusions.  SCEPTER QUARTZ – quartz  SMOKY crystal with scepter QUARTZ – brown to like protusion on black, “smoky” the end of the variety of Quartz. crystal that is wider than the rest of the crystal.  STAR QUARTZ – polished quartz  TOURMALINA displaying asterism TED QUARTZ – in the form of a six- quartz with splintery rayed star. tourmaline inclusions.  USES OF QUARTZ Quartz is an important mineral with numerous uses. Sand, which is composed of tiny Quartz pebbles, is the primary ingredient for the manufacture of glass. Transparent Rock Crystal has many electronic uses; it is used as oscillators in radios, watches, and pressure gauges, and in the study of optics. Quartz is also used as an abrasive for sandblasting, grinding glass, and cutting soft stones. It is also essential in the computer industry, as the important silicon semiconductors are made from Quartz. In addition to all the practical uses, Quartz is essential to the gem trade. Many varieties are faceted as gems. Amethyst and Citrine are the most well-known gem varieties. Rose Quartz, Smoky Quartz, Rock Crystal, and Aveturine are also cut or polished into gems. Small colorless Quartz crystals are worn by some as pendants for goodluck. Quartz is also a very popular among collectors. Certain collectors specialize their collection entirely on Quartz alone.  FELDSPAR Feldspar is the name of a large organization of rock- forming silicate minerals that make up over 50% of Earth’s 90 | P a g e crust. They are discovered in igneous, metamorphic, and sedimentary rocks in all components of the sector. Feldspar minerals have very comparable structures, chemical compositions, and bodily properties. Common feldspars consist orthoclase (KAISi3O8), albite (NaAISi3O8), and anorthite (CaAI2Si2O8).  COMPOSITIONS OF FELDSPAR GROUP MINERALS This group of minerals includes tectosilicates. Compositions of foremost elements in common place feldspars may be expressed in terms of 3 endmembers: potassium feldspar (K-spar) endmember KAISi3O8, albite endmember NaAISi3O8, anorthite endmember CaAI2SiO8. Solid answers between K-felspar and albite are referred to as “alkali feldspar”. Solid solutions among albite and anorthite are called “plagioclase”, or greater nicely “plagioclase feldspar”. Only constrained solid answer happens between K-feldspar and anorthite, and inside the two different stable answers, immiscibility occurs at temperatures common place in the crust of the Earth. Albite is taken into consideration both a plagioclase and alkali feldspar. CHEMICAL Silicate CLASSIFICATION COLOR Usually white, pink, gray or brown. Also, colorless, yellow, orange, red, black, blue, green. STREAK White LUSTER Vitreous. Pearly on some cleavage faces. DIAPHANEITY Usually translucent to opaque. Rarely transparent. Cleavage planes usually intersect at or close to a 90 CLEAVAGE degrees angle. Mohs HARDNESS 6 to 6.5 SPECIFIC GRAVITY 2.5 to 2.8 DIAGNOSTIC Perfect cleavage, with cleavage faces usually PROPERTIES intersecting at or close 90 degrees. Consistent hardness, specific gravity and pearly luster on cleavage. CHEMICAL A generalized chemical composition of X(Al,Si)4O8 , COMPOSITION where X is usually potassium, sodium, or calcium, but rarely can be barium, rubidium, or strontium. CRYSTAL SYSTEM Triclinic, monoclinic USES Crushed and powdered feldspar are important raw materials for the manufacture of plates glass, container glass, ceramic products, paints, plastics and many other products. Varieties of orthoclase, labradorite, oligoclase, microcline and other feldspar minerals have been cut and used as faceted and cabochon gems. PHYSICAL PROPERTIES OF FELDSPAR MINERAL  ALKALI FELDSPAR MINERALS The alkali feldspars are as follows: 91 | P a g e   Orthoclase (Monoclinic)  Sanidine (Monoclinic) (K,Na) KAISi3O8 AISi3O8  Microcline (Triclinic)  Anorthoclase (Triclinic) (Na, K) KAISi3O8 AISi3O8 Sanidine is stable at the highest temperatures, and microcline at the lowest. Perthite is a typical texture in alkali feldspar, due to exsolution of contrasting alkali feldspar compositions during cooling of an intermediate composition. The perthitic textures in the alkali feldspars of many granites can be seen with the naked eye. Microperthitic textures in crystals are visible using a light microscope, whereas cryptoperthitic textures can be seen only with an electron microscope.  BARIUM FELDSPARS Barium feldspars are also considered alkali feldspars. Barium feldspars form as the result of the substitution of barium for potassium in the mineral structure. The barium felspars are monoclinic and include the following:  Celsian BaAl2Si2O8,  Hyalophane BaAl2Si2O8.  PLAGIOCLASE FELDSPARS PLAGIOCL ASE PERCENT PERCENT MINERAL NaAlSi3O8 CaAl2Si2O8 NAME 100-90% 0-10% Albine albite anorthite 10-30% Oligoclase 90-70% albite anorthite Andesine 70-50% albite 30-50% 92 | P a g e  anorthite 50-70% Labradorite 50-30% albite anorthite 70-90% Bytownite 30-10% albite anorthite 90-100% Anorthite 10-0% albite anorthite The plagioclase feldspars are triclinic. The plagioclase series follows (with percent anorthite in parentheses): Albite (0 to 10) NaAISI3O8, Oligoclase (10 to 30) (Na, Ca) (AI, Si) AISi2O8, Andesine (30 to 50) NaAlSi3O8—CaAl2Si2O8, Labradorite (50 to 70) (Ca,Na)Al(Al,Si)Si2O8, Bytownite (70 to 90) (NaSi,CaAl)AlSi2O8, Anorthite (90 to 100) CaAl2Si2O8.  PRODUCTION AND USES OF FELDSPAR MINERALS About 20 million tonnes of feldspars have been produced in 2010, primarily by three countries: Italy (four.7 Mt), Turkey (4. Five Mt), and China (2 Mt). Feldspar is a common uncooked fabric utilized in glassmaking, ceramics, and to a point as a filler and extender in paint, plastics, and rubber. In glassmaking, alumina from feldspar improves product hardness, sturdiness, and resistance to chemical corrosion. In ceramics, the alkalis in feldspar (calcium oxide, potassium oxide, and sodium oxide) act as a flux, decreasing the melting temperature of a combination. Fluxes melt at an early stage in the firing method, forming a glassy matrix that bonds the opposite additives of the gadget collectively. In the US, approximately 66% of feldspar is consumed in glassmaking, including glass containers and glass fiber. Ceramics (inclusive insulators, sanitaryware, pottery, tableware, and tile) and different uses, which includes fillers, accounted for the remainder.  AUGITE Augite is isomorphous with the minerals Diopside and Hedenbergite. It is an intermediary member between these minerals, forming a series, but contains additional sodium and aluminum within its chemical structure. Strictly speaking, because of the variables in its chemical structure, Augite is really more of a group then a single mineral, but still classified a single mineral species by the IMA. 93 | P a g e  Augite is an important rock-forming mineral, and large crystals are fairly common. It is the most widespread member of the pyroxene group, and it frequently alters to many other minerals, including Hornblende, Chlorite, and Epidote. When altered to Actinolite, it is often called Uralite. Occasionally, though, it is found in large lustrous crystals which are sought after by mineral collectors. The name Augite is derived from the Greek word augites, “brightness”, in reference to the bright luster this mineral occasionally exhibits. PHYSICAL PROPERTIES OF AUGITE CHEMICAL (Ca,Na)(Mg,Fe,Al)(Al,Si)2O6 FORMULA COMPOSITION Silicate of calcium, sodium, magnesium, iron, and aluminum. Occasssionally with zinc, manganese, and titanium impurities. VARIABLE (Ca,Na)(Mg,Fe,Al,Zn,Mn,Ti)(Al,Si)2O6 FORMULA COLOR Green, grayish-green, greenish brown, dark brown, black STREAK Light green to colorless HARDNESS 5–6 CRYSTAL Monoclinic SYSTEM 3D CRYSTAL ATLAS CRYSTAL Often as prismatic crystals with a rectangular or octagonal FORMS AND cross section. Also in short, stubby crystals with a flattened AGGREGATES slightly pyramidal termination. Other forms are columnar, grainy, massive, fibrous, and in disordered aggregates of rectangular crystals. May also be in penetration twins with v-shaped saddles. Crystals from certain localities have partially hollow etchings. TRANSPARENC Opaque. Translucent in thin sections. Y SPECIFIC 3.2 – 3.6 GRAVITY LUSTER Vitreous, dull CLEAVAGE 1,2 – prismatic at cleavage angles of 87° and 93° (Characteristics of minerals in the pyroxene group). May also exhibit parting in one direction. FRACTURE Uneven to splintery TENACITY Brittle IN GROUP Silicates; Inosilicates; Pyroxene Group STRIKING Color, crystal habits, cleavage, and environment FEATURES ENVIRONMENT An important constituent of many igneous rocks, including 94 | P a g e  basalt, diabase, and gabbro. Also, in carbonatite and nepheline syenite pegmatites, and in metamorphic Serpentine deposits. ROCK TYPE Igneous, Metamorphic POPULARITY 2 (1-4) PREVALENCE 1 (1-3) DEMAND (1-3) 2 VARIETIES FASSAITE – variety of augite originally described from the Val D’ Fassa region in Italy which has a low iron content. This is usually responsible for this variety having a lighter green color and increased translucency then other most Augite. JEFFERSONITE – varieties of Augite rich in manganese and zinc, found in the Franklin District, Sussex Co., New Jersey and surrounding areas in the Franklin marble. Its chemical formula is Ca(Mn,Zn,Fe)Si2O6. URALITE – Pseudomorph of Actinolite after any mineral of the pyroxene group, especially Augite. USES OF AUGITE Augite does not have any physical, optical, or chemical properties that make it especially useful. It is therefore one of the few minerals that has no commercial use. The calcium content of augite has been found to be of limited use in studies of the temperature history of igneous rocks.  HORNBLENDE Hornblende is a group name used to describe Ferro- hornblende and Magnesio-hornblende, but the term is generally more inclusive for all calcium aluminum amphiboles. (Hornblende is frequently also used to describe any dark, opaque amphibole mineral without individual analysis.) The individual Hornblende minerals appear very similar and 95 | P a g e can be virtually indistinguishable without complex analysis, and are often just grouped under a Hornblende label without further distinguishing. Hornblende is major constituent of the earth and is extremely common. It forms in a host of different mineral environments, and is often a major constituent of the rock type it forms in. Hornblende is a rock-forming mineral, and it even constitutes its own rock type known as Horneblendite, a dark rock formed mostly from Hornblende. Hornblende is named after the German term horn, referring to its color, and blenden, meaning "deceiver", alluding to its habit of being confused with ore metals due to its dark color and luster. Its typical dark color and opacity are usually caused by iron in its structure.  HORNBLENDE AS A ROCK-FORMING MINERAL Hornblende is a rock-forming mineral that is an important constituent in acidic and intermediate igneous rocks such as granite, diorite, syenite, andesite, and rhyolite. It is also found in metamorphic rocks such as gneiss and schist. A few rocks consist almost entirely of hornblende. Amphibolite is the name given to metamorphic rocks that are mainly composed of amphibole mineral. Lamprophyre is an igneous rock that is mainly composed of amphibole and biotite with feldspar ground mass. PHYSICAL PROPERTIES OF HORNBLENDE CHEMICAL Silicate CLASSIFICATION COLOR Usually black, dark-green, dark-brown White, colorless – (brittle, often leaves cleavage STREAK debris behind instead of a streak) LUSTER Vitreous DIAPHANEITY Translucent to nearly opaque CLEAVAGE Two directions intersecting at 124 and 56 degrees Mohs HARDNESS 5 to 6 96 | P a g e SPECIFIC GRAVITY 2.9 to 3.5 (varies depending upon composition) DIAGNOSTIC Cleavage, color, elongate habit PROPERTIES CHEMICAL (Ca,Na)2–3(Mg,Fe,Al)5(Al,Si)8O22(OH,F)2 COMPOSITION CRYSTAL SYSTEM Very little industrial use USES USES OF HORNBLENDE The mineral hornblende has very few uses. Its primary use might be as a mineral specimen. However, hornblende is the most abundant mineral in a rock known as amphibolite which has a large number of uses. It is crushed and used for highway construction and as railroad ballast. It is cut for use as dimension stone. The highest quality pieces are cut, polished, and sold under the name "black granite" for use as building facing, floor tiles, countertops, and other architectural uses. Hornblende has been used to estimate the depth of crystallization of plutonic rocks. Those with low aluminum content are associated with shallow depths of crystallization, while those with higher aluminum content are associated with greater depths of crystallization. This information is useful in understanding the crystallization of magma and also useful for mineral exploration.  BIOTITE Biotite is a very common form of mica. It is named in honor Jean Baptiste Biot (1774 - 1862), a French physicist, mathematician, and astronomer who researched the mica minerals for their optical properties. Because of Biotite's abundance, its presence is usually lacking in collections except for it being an accessory mineral to other minerals. Biotite can come in enormous crystal sheets that can weigh several hundred pounds. Thin sheets can be peeled off as layers, and the thinner a layer is peeled the greater its transparency becomes. In 1998, the IMA removed the status of Biotite as an individual mineral species, and instead declared it as a group name for the following individual members: Phlogopite, Annite, Siderophyllite, and Eastonite. However, mineral collectors still refer to Biotite by its traditional name and rarely make a distinction among its members except for Phlogopite. Biotite is very hard to clean because if washed it will absorb water internally and start to break apart. The best way to wash Biotite and other Micas is with a dry electric toothbrush. PHYSICAL PROPERTIES OF BIOTITE CHEMICAL The classic formula for Biotite is: FORMULA K(Mg,Fe2+3)(Al,Fe3+)Si3O10(OH,F)2 97 | P a g e  The group formula including all member minerals: K(Mg,Fe2+)3(Al,Fe3+)[(Al,Si)3O10](OH,F)2 Individual members are: Phlogopite: KMg3AlSi3O10)(F,OH)2 Siderophyllite: KFe2+2Al(AlSi2O10)(OH)2 Eastonite: KMg2Al(AlSi2O10)(OH)2 Annite: KFe2+3AlSi3O10(OH)2 Fluorannite: KFe2+3AlSi3O10)F2 Tetraferriannite: K(Fe2+3Mg)(Fe3+,Al)Si3O10)(OH)2 Basic fluoro potassium, magnesium, iron aluminum COMPOSITION silicate Black, dark brown, dark green, reddish black. Individual COLOR group member minerals such as Phlogopite and Eastonite can be in lighter colors. STREAK White HARDNESS 2.5 – 3 CRYSTAL Monoclinic SYSTEM 3D CRYSTAL ATLAS CRYSTAL Crystals are in thick flakes, micaceous masses and FORMS AND groupings, and in tabular, foliated, flaky, and scalyforms. AGGREGATES Crystals may also be elongated with one dimension flat, or stubby triangular or hexagonally shaped crystals. Also forms in prismatic barrel-shaped or tapered pyramid- shaped crystals composed of dense parallel plates, and as rounded nodules of dense crystals. TRANSPARENC Translucent to opaque. Thin flakes will always be Y translucent if held up to the light. SPECIFIC 2.8 – 3.4 GRAVITY LUSTER Pearly CLEAVAGE 1, 1 FRACTURE Uneven TENACITY Sectile, elastic OTHER ID Tendency for small pieces or flakes or peel off. MARKS IN GROUP Silicates; Phyllosilicates; Mica Group STRIKING Flaky habit, crystals, sectility, and mode of occurence FEATURES ENVIRONMENT Biotite is a common rock-forming mineral, and is especially noted in metamorphic rocks such as schist and gneiss. It is also found in igneous rock such as granites and rhyolites. Biotite is also the primary mica in rare earth pegmatites. 98 | P a g e ROCK TYPE Igneous, Metamorphic POPULARITY 2 (1-4) PREVALENCE 1 (1-3) DEMAND (1-3) 2 VARIETIES MANGANOPHYLLITE Manganese-rich variety of Biotite.  MUSCOVITE Muscovite is the most common mineral of the mica family. It is an important rock-forming mineral present in igneous, metamorphic, and sedimentary rocks. Like other micas it readily cleaves into thin transparent sheets. Muscovite sheets have a pearly to vitreous luster on their surface. If they are held up to the light, they are transparent and nearly colorless, but most have a slight brown, yellow, green, rose-color tint. The ability of muscovite to split into thin transparent sheets – sometimes up to several feet across – gave it an early use as window panes. In the 1700s, it was mined for this use from pegmatites in the area around Moscow, Russia. These panes were called “muscovy glass” and that term is thought to have inspired the mineral name “muscovite”. PHYSICAL PROPERTIES OF MUSCOVITE CHEMICAL KAl3Si3O10(OH)2 FORMULA Basic potassium aluminum silicate, sometimes with some COMPOSITION chromium or manganese replacing the aluminum VARIABLE K(Al,Cr,Mn)3Si3O10(OH)2 FORMULA Colorless, white, beige, yellow, brown, gray, green, pink, COLOR purple, red, black; occasionally multicolored STREAK Colorless HARDNESS 2 – 2.5 CRYSTAL Monoclinic SYSTEM 99 | P a g e 3D CRYSTAL ATLAS CRYSTAL Crystals are in thick flakes, micaceous masses and FORMS AND groupings, and in tabular, foliated, flaky, and scaly forms. AGGREGATES Crystals may also be elongated with one dimension flat, or stubby triangular or hexagonally shaped crystals. Muscovite also forms interesting aggregates of dense bladed crystals, thick rosettes, uniquely twinned star-shaped formations, and rounded botryoidal and globular masses of dense flakes. Muscovites may also form pseudomorphs after other minerals, assuming the original crystal shape. TRANSPARENC Transparent to translucent Y SPECIFIC 2.7– 3.0 GRAVITY LUSTER Pearly CLEAVAGE 1, 1 FRACTURE Uneven TENACITY Sectile, Elastic OTHER ID Tendency for small pieces or flakes or peel off. MARKS IN GROUP Silicates; Phyllosilicates; Mica Group STRIKING Flaky habit, crystals, sectility, and mode of occurrence FEATURES ENVIRONMENT Muscovite is a very common rock-forming mineral and is important constituent in many environments. Its presence is noted especially in granite pegmatites, in contact metamorphic rocks, in metamorphic schists, and in hydrothermal veins. Important muscovite deposits where large significant crystals occur are almost exclusively from granite pegmatites. ROCK TYPE Igneous, Metamorphic POPULARITY (1- 1 4) PREVALENCE 1 (1-3) DEMAND (1-3) 1 CHEMICAL COMPOSITION Muscovite is a potassium-rich mica with the following generalized composition; 100 | P a g e In this formula potassium is sometimes replaced by other ions with a single positive charge such as sodium, rubidium, or cesium. Aluminum is sometimes replaced by magnesium, iron, lithium, chromium, or vanadium. When chromium substitutes for aluminum in muscovite the material takes on a green color and is known as “fuchsite. Fuchsite is often found disseminated through metamorphic rocks of the greenschist facies. Occasionally, it will be abundant enough to give the rock a distinct green color, and for those rocks the name “verdite” is used. USES OF GROUND MICA Muscovite is a very poor conductor of heat and electricity, and is thus used as an insulator for various electrical products and semiconductors. It is also used in the production of automotive tires and cosmetics. Large Muscovite sheets were also once used for oven windows ("isinglass") due to their ability to withstand high temperatures and keep the heat inside. VARIETIES OF MUSCOVITE  ALURGITE – manganese-rich, pink to red variety of Muscovite.  FUCHSITE – dark green, chromium-rich variety of Muscovite. Named in honor of German professor and mineralogist Johann Nepomuk von Fuchs (1774 – 1856).  MARIPOSITE – green form of Muscovite mica in small dense flake group found in Mariposa (and Tuolome) County, Califormnia. Mariposite forms in metamorphosized Dolomite and Quartz, and these are usually present as veins or as a base material. A combination of the green mica and the veins or base material forms a rock which is also called Mariposite, and it is sometimes used as an ornamental stone.  SCHERNIKITE – a light pink form of Muscovite.  SERICITE – a fine-grained form of mica, usually Muscovite, that is somewhat silky in appearance. 101 | P a g e   STAR MUSCOVITE – describes twinned Muscovite crystals in pointed star-shaped sections.  CALCITE Calcite is a rock-forming mineral with a chemical formula of CaCO3. It is extremely common and found throughout the world in sedimentary, metamorphic, and igneous rocks. Some geologists consider it to be a “ubiquitous mineral” – one that is found everywhere. Calcite is the principal constituent of limestone and marble. These rocks are extremely common and make up a significant portion of Earth’s crust. They serve as one of the largest carbon repositories on our planet. The properties of calcite make it one of the most widely used mineral. It is used as a construction material, abrasive, agricultural soil treatment, construction aggregate, pigment, pharmaceutical and more. It has more uses than almost any other mineral. CALCITE AS LIMESTONE AND MARBLE Limestone is a sedimentary rock that is composed primarily of calcite. It forms from both the chemical precipitation of calcium carbonate and the transformation of shell, coral, fecal and algal debris into calcite during diagenesis. Limestone also forms as a deposit in caves from the precipitation of calcium carbonate. Marble is a metamorphic rock that forms when limestone is subjected to heat and pressure. A close examination of a broken piece of marble will usually reveal obvious cleavage faces of calcite. The size of the calcite crystals is determined by the level of metamorphism. Marble that has been subjected to higher levels of metamorphism will generally have larger calcite crystals. 102 | P a g e USES OF CALCITE The construction industry is the primary consumer of calcite in the form of limestone and marble. These rocks have been used as dimension stones and in mortar for thousands of years. Limestone blocks were the primary construction material used in many of the pyramids of Egypt and Latin America. Today, rough and polished limestone and marble are still an important material used in prestige architecture. Modern construction uses calcite in the form of limestone and marble to produce cement and concrete. These materials are easily mixed, transported, and in placed in the form of a slurry that will harden into a durable construction material. Concrete is used to make buildings, highways, bridges, walls, and many other structures. PHYSICAL PROPERTIES OF CALCITE CHEMICAL CaCO3 FORMULA Calcium cacrbonate, sometimes with impurities of iron, COMPOSITION magnesium, or manganese, and occasionally zinc and cobalt. VARIABLE (Ca,Fe,Mg,Mn,Zn,Co)CO3 FORMULA Colorless, white, yellow, brown, orange, pink, red, purple, COLOR blue, green, gray, black, may also be multicolored or banded. STREAK White HARDNESS 3 CRYSTAL Hexagonal SYSTEM 3D CRYSTAL ATLAS CRYSTAL Occurs in a great variety of shapes, with the most common FORMS AND forms asrhombohedral and scalenohedralcrystals. Crystals AGGREGATES may be tabular, acicular, prismatic, flaky, and needle-like. May occur as bundles of scalenohedrons, intergrown rhombohedrons, hair-like masses of acicular crystals, grainy, stalactitic, fibrous, massive, 103 | P a g e  and earthy. Scalenohedral twinning is common. TRANSPARENC Transparent to opaque Y SPECIFIC 2.7 GRAVITY LUSTER Vitreous CLEAVAGE 1, 3 – rhombohedal FRACTURE Conchoidal. Rarely observed due to the perfect cleavage TENACITY Brittle OTHER ID 1) Commonly fluorescent; specimens from different MARKS localities fluoresce different colors. Some calcite is also phosphorescent. 2) Transparent crystals exhibit strong double refreaction. 3) May be thermoluminescent. COMPLEX 1) Effervescent in hydrochloric acid and most other acids. TESTS 2) Calcite that doesn’t fluoresce usually becomes fluorescent upon heating. IN GROUP Carbonates; Calcite Group STRIKING Hardness, cleavage, fluorescence, and effervescence with FEATURES hydrochloric acid. ENVIRONMENT Calcite is a constituent of all mineral environment, including sedimentary, igneous, and metamorphic. ROCK TYPE Igneous,cSedimentary, Metamorphic POPULARITY (1- 1 4) PREVALENCE 1 (1-3) DEMAND (1-3) 1 VARIETIES OF CALCITE  AGARIC  ANTHRACO MINERAL – NITE – dark gray crumbly white to black variety of calcite found calcite with a on cavern bitumen coating or floors near inclusions. stalagmites and stalactites.  COBALT  DOGTOOTH CALCITE – calcite in OCALCITE – groupings of thick and pointy refers to an scalenohedral crystals. intermediary mineral between Calcite and Sphaerocobaltite in a solid solution 104 | P a g e  series. It is most often perceived as a cobalt-rich variety of Calcite with a rich pink color.  FLOWSTO  ICELAND NE – calcite SPAR – large, formed by transparent, mineral-rich colorless to lightly water that colored, deposits the rhombohedral dissolved mineral on the walls of variety of Calcite. caverns and cliffs, forming a Double refraction is especially noted smooth and humpy growth. in Iceland Spar crystals.  ONYX  SALMON MARBLE – CALCITE – orange- travertine or tufa red, “salmon” colored in the mineral variety of Calcite form of Aragonite that is usually or Calcite that opaque. exhibits color banding.  SAND  STALACTITE – icicle-like mineral CALCITE – calcite formation found that trapped on the roof of particles of sand caverns, created in its interior when mineral- when it formed. rich water drips down and the dissolved mineral accumulates into the icicle-like formation.  STALAGMITE – tall, domed  TRAVERTINE – mounds of calcium mineral formation carbonate found on the roof formed from of caverns, created hot springs when mineral-rich that contain water drips down calcium-rich and the dissolved mineral water that accumulates into the icicle-like bubbles up to formation. the earth and cools down, and its capability to hold calcium is reduced. The water eliminates the calcium, the calcium forms a growing mound of calcium carbonate, which is porous. Travertine is usually Aragonite, although it may also be calcite. 105 | P a g e   TUFA – aragonite formed from precipitating water that traps in organic matter, such as leaves, twigs, and moss. Also, calcareous mounds formed from deposition of hot springs that trap in organic matter.  GARNET Garnet is the name used for a large group of rock-forming minerals. It is not a single mineral, but a group contains related, isomorphous minerals that form a series with each other. The garnet members form intermediary minerals between each member, and may even intergrow within a single crystal. The garnets vary only slightly in physical properties, and some of the members so similar that they are indistinguishable from one another without x-ray analysis. The common Garnets can be divided into two subgroups: Group 1: Garnets containing aluminum (Al) as their second element. These include Pyrope, Almandine, and Spessartine. ("Pyralspite") Group 2: Garnets containing calcium (Ca) as their first element. These include Uvarovite, Grossular, and Andradite. ("Ugrandite") The members of each group freely intermingle among one another. For example, the magnesium in Pyrope may be partially replaced by some iron from Almandine or by some manganese from Spessartine. However, between the two groups, it is much rarer for them to intermingle. 106 | P a g e   GARNET PHYSICAL AND CHEMICAL PROPERTIES The most commonly encountered minerals in the garnet group include almandine, pyrope, spessartine, andradite, grossular, and uvarovite. They all have a vitreous luster, a transparent-to-translucent diaphaneity, a brittle tenacity, and a lack of cleavage. They can be found as individual crystals, stream-worn pebbles, granular aggregates, and massive occurrences. Their chemical composition, specific gravity, hardness, and colors are listed below. As seen above, there are variety of different types of garnet, and each has a different chemical composition. There are solid solution series between most of the garnet minerals. This wide variation in chemistry determines many of their physical properties. As an example, the calcium garnets generally have a lower specific gravity, a lower hardness and are typically green in color. In contrast, the iron and manganese garnets have a higher specific gravity, a greater hardness and are typically red in color. HOW DOES GARNET FORM?  GARNET IN METAMORPHIC ROCKS Most garnet forms at convergent plate boundaries where shale is being acted upon by regional metamorphism. The heat and pressure of metamorphism breaks chemical bonds and causes minerals to recrystallize into structures that are stable under the new temperature-pressure environment. The aluminum garnet, almandine, generally forms in this environment. As these rocks are metamorphosed, the garnets start as tiny grains and enlarge slowly over time as metamorphism progresses. As they grow, they displace replace, and include the surrounding rock materials. The photo below shows a microscopic view of a garnet grain that has grown within a schist matrix. It included a number of the rock’s mineral 107 | P a g e grains as it grew. This explains why so many garnets formed by regional metamorphism are highly included. The calcium garnets typically form when argillaceous limestone is altered into marble by contact metamorphism along the edges of igneous intrusions. These are andradite, grossular, uvarovite, the slightly softer, typically green garnets are highly regarded in the gem trade; they are tsavorite (a bright green grossular) and demantoid (a golden-green andradite).  GARNET IN IGNEOUS ROCKS Garnet often occurs as an accessory mineral in igneous rocks such as granite. May people are familiar with almandine garnet because it is sometimes seen as dark red crystals in the igneous rock used as granite countertops. Spessartine is an orange garnet found as crystals in granite pegmatites. Pyrope is a red garnet that is brought to Earth’s surface in pieces of peridotite that were torn from the mantle during deep-source volcanic eruptions. Garnet is also found in basaltic lava flows.  GARNET IN SEDIMENTARY ROCKS AND SEDIMENTS Garnet are relatively durable minerals. They are often found concentrated in the soils and sediments that form when garnet-bearing rocks are weathered and eroded. These alluvial garnets are often the target of mining operations because they are easy to mine and remove from the sediment/soil by mechanical processing. 108 | P a g e   USES OF GARNET Garnet has been used as gemstone for thousands of years. In the past 150, it has seen many additional uses of garnet in the United States. Garnet is also used as an indicator mineral during mineral exploration and geologic assessments. QUESTIONS: 1.What is the name of a large organization of rock-forming silicate minerals that make up over 50% of Earth’s crust? 2.What are the 3 varieties Of Augite? Explain each. 3.What do you call a rock-forming mineral with a chemical formula of CaCO 3? 109 | P a g e LESSON 3: PROPERTIES, PROCESS OF FORMATION OF ALL MINERALS Formation of Minerals To grow a mineral crystal, the elements needed to make it must be present in the appropriate proportions, the physical and chemical conditions must be favourable, and there must be sufficient time for the atoms to become arranged. Physical and chemical conditions include factors such as temperature, pressure, presence of water, pH, and amount of oxygen available. Time is one of the most important factors because it takes time for atoms to become ordered. If time is limited, the mineral grains will remain very small. The presence of water enhances the mobility of ions and can lead to the formation of larger crystals over shorter time periods. Most of the minerals that make up the rocks around us formed through the cooling of molten rock, known as magma. At the high temperatures that exist deep within Earth, some geological materials are liquid. As magma rises up through the crust, either by volcanic eruption or by more gradual processes, it cools and minerals crystallize. If the cooling process is rapid, the components of the minerals will not have time to become ordered and only small crystals can form before the rock becomes solid. The resulting rock will be fine-grained. If the cooling is slow, the degree of ordering will be higher and relatively large crystals will form. In some cases, the cooling will be so fast that the texture will be glassy, which means that no crystals at all form. Volcanic glass is not composed of minerals because the magma has cooled too rapidly for crystals to grow, although over time the volcanic glass may crystallize into various silicate minerals. Minerals can also form in several other ways:  Precipitation from aqueous solution  Precipitation from gaseous emanations  Metamorphism — formation of new minerals directly from the elements within existing minerals under conditions of elevated temperature and pressure  Weathering — during which minerals unstable at Earth’s surface may be altered to other minerals  Organic formation — formation of minerals within shells (primarily calcite) and teeth and bones (primarily apatite) by organisms (these organically formed minerals are still called minerals because they can also form inorganically) 110 | P a g e  Opal is a mineraloid, because although it has all of the other properties of a mineral, it does not have a specific structure. Pearl is not a mineral because it can only be produced by organic processes.  Mineral Properties Minerals are universal. A crystal of hematite on Mars will have the same properties as one on Earth, and the same as one on a planet orbiting another star. That’s good news for geology students who are planning interplanetary travel since we can use those properties to help us identify minerals anywhere. That doesn’t mean that it’s easy, however; identification of minerals takes a lot of practice. Some of the mineral properties that are useful for identification are as follows: Colour Streak Lustre Hardness Habit Cleavage/fracture Density Other  Colour For most of us, colour is one of our key ways of identifying objects. While some minerals have particularly distinctive colours that make good diagnostic properties, many do not, and for many, colour is simply unreliable. The mineral sulphur is always a distinctive and unique yellow. Hematite, on the other hand, is an example of a mineral for which colour is not diagnostic. In some forms hematite is deep dull red, but in others it is black and shiny metallic. Many other minerals can have a wide range of colours. In most cases, the variations in colours are a result of varying proportions of trace elements within the mineral. In the case of quartz, for example, yellow quartz has trace amounts of ferric iron (Fe3+), rose quartz has trace amounts of manganese, purple quartz (amethyst) has trace amounts of iron, and milky quartz, which is very common, has millions of fluid inclusions (tiny cavities, each filled with water).  Streak In the context of minerals, “colour” is what you see when light reflects off the surface of the sample. One reason that colour can be so variable is that the type of surface is variable. If we grind a small amount of the sample to a powder we get a much better indication of its actual colour. This can easily be done by scraping a corner of the sample across a streak plate (a piece of unglazed porcelain). The result is that some of the mineral gets ground to a powder and we can get a better impression of its “true” colour. The streak colours of earthy hematite and specular hematite. Although the specular hematite streak looks close to black, it does have red undertones that you can see if you look closely.  Lustre Lustre is the way light reflects off the surface of a mineral, and the degree to which it penetrates into the interior. The key distinction is between metallic and non- metallic lustres. Light does not pass through metals, and that is the main reason they look 111 | P a g e “metallic.” Even a thin sheet of metal such as aluminum foil will prevent light from passing through it. Many non-metallic minerals may look as if light will not pass through them, but if you take a closer look at a thin edge of the mineral you can see that it does. If a non-metallic mineral has a shiny, reflective surface, then it is called “glassy.” If it is dull and non-reflective, it is “earthy.” Other types of non-metallic lustres are “silky,” “pearly,” and “resinous.” Lustre is a good diagnostic property, since most minerals will always appear either metallic or non-metallic.  Hardness One of the most important diagnostic properties of a mineral is its hardness. In 1812 German mineralogist Friedrich Mohs came up with a list of 10 reasonably common minerals that had a wide range of hardness. In fact, while each mineral on the list is harder than the one before it, the relative measured hardnesses (vertical axis) are not linear. For example apatite is about three times harder than fluorite and diamond is three times harder than corundum. Some commonly available reference materials are also shown on this diagram, including a typical fingernail a piece of copper wire a knife blade or a piece of window glass, a hardened steel file, and a porcelain streak plate. These are tools that a geologist can use to measure the hardness of unknown minerals.  Crystal Habit When minerals form within rocks, there is a possibility that they will form in distinctive crystal shapes if they are not crowded out by other pre-existing minerals. Every mineral has one or more distinctive crystal habits, but it is not that common, in ordinary rocks, for the shapes to be obvious. Quartz, for example, will form six-sided prisms with pointed ends, but this typically happens only when it crystallizes from a hot water solution within a cavity in an existing rock. Pyrite can form cubic crystals but can also form crystals with 12 faces, known as dodecahedra (“dodeca” means 12). Because beautiful well-formed crystals are rare in ordinary rocks, habit isn’t as useful a diagnostic feature as one might think. However, there are several minerals for which it is important. One is garnet, which is common in some metamorphic rocks and typically displays the dodecahedral shape. Another is amphibole, which forms long thin crystals, and is common in igneous rocks like granite. Mineral habit is often related to the regular arrangement of the molecules that make up the mineral. Some of the terms that are used to describe habit include bladed, botryoidal (grape-like), dendritic (branched), drusy (an encrustation of minerals), equant (similar in all dimensions), fibrous, platy, prismatic (long and thin), and stubby.  Cleavage and fracture Crystal habit is a reflection of how a mineral grows, while cleavage and fracture describe how it breaks. These characteristics are the most important diagnostic features of many minerals, and often the most difficult to understand and identify. Cleavage is what 112 | P a g e we see when a mineral breaks along a specific plane or planes, while fracture is an irregular break. Some minerals tend to cleave along planes at various fixed orientations; some do not cleave at all (they only fracture). Minerals that have cleavage can also fracture along surfaces that are not parallel to their cleavage planes. Quartz has no cleavage because it has equally strong Si –O bonds in all directions, and feldspar has two cleavages at 90° to each other. One of the main difficulties with recognizing and describing cleavage is that it is visible only in individual crystals. Most rocks have small crystals and it’s very difficult to see the cleavage within a small crystal. Geology students have to work hard to understand and recognize cleavage, but it’s worth the effort since it is a reliable diagnostic property for most minerals.  Density Density is a measure of the mass of a mineral per unit volume, and it is a useful diagnostic tool in some cases. Most common minerals, such as quartz, feldspar, calcite, amphibole, and mica, have what we call “average density” (2.6 to 3.0 g/cm3), and it would be difficult to tell them apart on the basis of their density. On the other hand, many of the metallic minerals, such as pyrite, hematite, and magnetite, have densities over 5 g/cm 3. They can easily be distinguished from the lighter minerals on the basis of density, but not necessarily from each other. A limitation of using density as a diagnostic tool is that one cannot assess it in minerals that are a small part of a rock with other minerals in it. Other properties Several other properties are also useful for identification of some minerals. For example, calcite is soluble in dilute acid and will give off bubbles of carbon dioxide. Magnetite is magnetic, so will affect a magnet. A few other minerals are weakly magnetic. QUESTIONS: 1. What are the different types of mineral properties? 2. How is minerals formed? 3. Why is colour not necessarily a useful guide to mineral identification? 113 | P a g e LESSON 4: COAL AND PETROLEUM  COAL Coal are hard rock which can be burned as solid fossil fuel. They are mostly carbon and also contains hydrogen, sulphur, oxygen, and nitrogen. They are sedimentary rock formed from bog, by the pressure of rocks it suddenly go down. Peat or bogs, and therefore coal, are formed from the remains of plants which lived many years ago in tropical ground such as those of the late Carboniferous period or Paleozoic era. Like in Philippines, they do also wood heated in an airless space which can make charcoal, which is like coal. Coal can burned for energy or heat. Some of the coal mined today is burned in power stations to make electricity. Coal are fossil fuel and are the altered remains of ancient vegetation that originally accumulated in sump and peat bogs. The energy we get from coal today comes from energy that plants taken into the sun. Formation of coals In the period of the Paleozoic era, land was covered with swamps filled with huge trees and leafy plants.As the trees and plants died, they drop to the bottom of the bog of oceans to form layers of spongy materials called peat. Over a many years, peat was covered by sand, the clay turned into sedimentary rocks. More rock stack on top of old rock and began to press on the peat. It was press and turned into fossil fuels.  Coke Coke is virtually pure form of carbon. Coke is a porous, black and the same as the coal. Coke have high percentage of the carbon and low in impurities, and it is reached from destructive distillation of a selective type of coal. Coal can be heated very hot in a place where there is no oxygen or what we called the airless space to produce coke. Coke can be used in smelting to reduce metals from their minerals. It is used in producing of steel and in the extraction of many types of metals.  Coal Tar Coal tar is reached as one of the by-products is obtaining the coke or the what we called coal gas. Coal tar is a highly viscous kind of liquid and is brown-black in color. Coal tar is a inconstant mixture of many substances. It is used to in producing of many product like synthetic dyes, explosive, perfumes, roofing materials, drugs, plastics and many more. 114 | P a g e It is almost about 20 years ago, when coal tar was used as a binding materialin making of the roads. But presently we are using bitumen to substitute in coal tar in making the roads.  Coal Gas The coal gas is one of the by-products in processing of the coke. It is used as fuel basically for heating in many industries. Types of Coal  PEAT is a fibrous, soft, and spongy substance which plant remains are easily recognizable. They contain a large amount of water and must be dry before use.  LIGNITE are formed when peat are subjected to increased vertical pressure from accumulating sediments. Lignite are the dirtiest coal and are used as fuel for electric power generation. It is the softest and the lowest in carbon but high in hydrogen and oxygen content.  BITUMINOUS COAL are dense rock, black but sometimes dark brown and are greatly used in industry as a source of heat energy. And it is in between of anthracite and lignite.  SUB-BITUMINOUS COAL are used as fuel for steam-electric power generation.  STEAM COAL are used as a fuel for steam locomotives. The small steam coal are used as a fuel for domestic water heating.  ANTHRACITE also known as hard coal and more carbon because it’s hard and has a high lustre. A harder, glossy, black coal. It’s longer burning, and used mainly for residential and commercial space heating.  PETROLEUM Petroleum is a natural liquid found below the Earth’s surface that can be refined into fuel. Petroleum is a fossil fuel, that it has been created by the decomposition of organic matter over many years. It is formed in sedimentary rock under in the intense heat and pressure. Petroleum is used as fuel to power vehicles, heating units, and machines of all sorts, and also being converted into plastics and other materials. Because of worldwide reliance on petroleum, the petroleum industry is extremely powerful and it is a major influence on world politics and the global economy. Formation of Petroleum Small sea plants and sea animals died and are burried on the sea or ocean floor for many years. As the years pass by, the died plants and animals in the ocean were covered 115 | P a g e by the layers of sand and silt. As million years pass, the remains were burried extending far downwards. And because of the high pressure and temperature on water the dead organisms were transformed to petroleum. The petroleum is also known as the fossil fuels because it is product of the dead organisms. Exraction of Petroleum Petroleum and the extraction and processing of this drive the world economy and global politics. The world owes its existence to petroleum. There are some of largest companies in the world that are involved in the extraction and processing of the petroleum, with other companies creating products which require hydrocarbons to operate or a petroleum-based. Asphalt, which is used to pave highways, is also made from petroleum. Vehicles which drive on highways are made on materials that derived from petroleum and run on fuels refined from petroleum. Petroleum is most frequently related with crude oil and the wells dug into the ground to bring that liquid to the surface. The liquid can vary in color, from relatively transparent to dark brown or black. Heavier oils are usually the darkest in color. Petroleum contains various types of hydrocarbons, and natural gas is commonly found dissolved in the liquid in essential amounts. Hydrocarbons can be processed in refineries into different types of fuels. Hydrocarbon molecules in petroleum are include asphalt, paraffin, and naphthene. Petroleum are comprised of a mixture of various hydrocarbons, and it can have a different chemical and physical properties depending on where it is found in the world. The more dense of the petroleum the more difficult it is to process and the less valuable it is. The light crude is the easiest to refine and are generally considered as the most valuable, while the viscosity of the heavy crude can make it more expensive to refine. And the sour crude contains the sulfur and sulfuric compounds, which can make the fuel less valuable. In petroleum industry, petroleum companies are divided into upstream, midstream and downstream. Upstream which deals with crude oil. Midstream which bring up to the storage and transport of crude oil and other more refined products. And downstream refers to products for consumers such as gasoline. Refining of Petroleum When the extraction was done, the petroleum was refined to reached petrol, diesel, wax, bitumen, kerosene, paraffin, lubricating oil, and many more. Petroleum refinery is the place where the refining process of the petroleum performed. Here are some of the petroleum products and their uses:  Petrol - fuels the motor car, solvent in dry cleaning, and aeronautics.  Diesel - can fuels the heavy vehicle, like trucks, rail engine and small vehicle like vans, jeep, jet aircraft, small generators, and many more.  Bitumen - is used to make roads, paints and many more. 116 | P a g e  Kerosene - it fuels gas stoves, lamps, jet aircraft and many more.  Parrafin - can use in producing an ointment, cosmetics, and even candles, and many more.  Lubricating oil - is used as a lubricants in engines.  Liquid Petroleum Gas - it fuels vehicle, and fuel in household. QUESTIONS: 1. What are the disadvantages and advantages of the coal to the environment? 2. What is the role of the coal to have a cleaner, healthier energy future? 3. What are the environmental impacts of the petroleum? 117 | P a g e LESSON 5: THEIR ORIGIN AND OCCURRENCE IN INDIA An appraisal of the total minimum resources of India so far known to geologist brings home that the mineral wealth of India is not inconsiderable for a country of her size and population that it encompasses a sufficient range of useful products that are necessary to make a modern civilized country more or less industrially self-contained. Except in the case of minerals such as iron-ore, aluminum-ore, titanium-ore, mica and a few other minerals, the resources in econo mic minerals and metals are however, limited. Chances of discovery of new minerals deposits of any extent and richness by ordinary geological methods are not many, though the recent geophysical methods of locating underground mineral occurrences by electrical, magnetic, gravimetric and acismic methods seem to offer possibilities of bringing to light hitherto undiscovered but, in some cases, suspected deposits of petroleum, coal-measures, natural gas, underground water, metallic lodes, etc. Nature has made a very unequal territorial distribution of minerals in Indian region. The vast alluvial plains tract of Northern India is devoid of mines of economic minerals. The Archaean terrain of Bihar and Orissa, possesses the largest concentration of ore such as iron, manganese, copper, thorium, uranium, aluminum, chromium, industrial minerals like mica, sillimanite, phosphate; and over three-fourths of India’s reserves of coal including coking coal. The iron-ore reserves lying in one or two districts of Bihar and in the adjoining territories of Orissa are calculated at over 8,000 million tons, surpassing in richness and extent those of any known region. There are large reserves of manganese- ores; over 50 percent of the world’s best mica – block, splitting and sheet – is a supplied by the mica mines of Kodorma and Gaya in Bihar. The second minerally rich state is Madhya Pradesh, carrying good reserves of iron and manganese ores, coal, limestone and bauxite. Madras has workable deposits of iron, manganese, magnesite, mica, limestone, and Lignite. Mysore state has yielded all the gold of India, besides producing appreciable quantities of iron, porcelain clays and chrome-ores. Hyderabad has good reserves of second grade coal, besides being potential source of several industry minerals. Kerala processes enormous concentrations of heavy minerals and high strategic importance calculated to contain, together with lesser deposits along the Malakar coast, some 200 million tons of ilmenite, besides monatize, zircon and garnet in workable quantities. The state of Uttar Pratlesh and (Eastern) Prajab have been far less productive and have scarcely as yet figure its India statistics. Rajasthan, for a long time absent in India’s mineral returns, gradually be a productive centre, holding protnise for the future in non metal ( copper, lead and zinc), uranium, mica, steatite and precious stones ( aquamarine and emerald). West Bengal’s mineral resources are confined to coal ( annual mineral capacity about 16 million tons) and iron ore of the Himlayan region, the only proved mineralized region of importance is the territory of Kashmir south of the great himlayan axis, with its coal (some of it anthracitic), aluminum ore, sapphires and some minor industrial minerals. But for the large magnesitereservesand partly known copper deposits of Kumaon and Sikkim 118 | P a g e and some fairly wide spread bodies of iron-ore in these area, the rest of the Himlayan region is vertable terra incognita as regards economic minerals. The same is applicable to Sikkim and Bhutan region. Nepal can considered a fairly mineralized terrain where occurrences of cobalt, nickel and copper-re are reported, but which has not yet been fully explored geologically. The rock- system of India possess in varying degrees most of the minerals and metals. The various useful products they yield, their detailed occurrences, and some facts regarding the production of the most important ones are dealt with the foollowingchapters. About 86 varieties of economically important minerals re found in India They are:  10 metallic minerals  46 non-metallic minerals ( industrial)  3 atomic minerals and  23 minor minerals ( including building and other materials)  4 fuel minerals. The economy of India is controlled by two vital resources  Metallic and non-metallic mineral resources  Mineral fuels While studying the economic geography of India, all these aspects are to be studied in details, because, these two resources control many of the industrial activities. If we look at the mines operating in India, we have  2999 mines working on all minerals  574 mines working on coal  700 mines concentrating on metallic minerals and  1725 mines working for getting non-metallic minerals. The are six core industries controlling the national economy of India. They are: 1. Crude oil 2. Petroleum 119 | P a g e  3. Coal 4. Electricity 5. Cement 6. Finish carbon steel All of these are supported by mining sector. This in turn depends on mineral resources. Among the resources, minerals are the major contributors of the national economy. India is the country, much dependant on the available natural resources for its economy. India has a good amount of natural resources like water resources, forest resources, energy resources, mineral resources, land resources and the human resources. QUESTIONS: 1. How many varieties of economically important minerals in India? 2. What are the minerals found in India? 3. What are the six core industries controlling the national economy of India? 120 | P a g e