Week 1 Compilation PDF

Minerals  MINERALOGY WHAT IS MINERALOGY? It is the study of naturally occurring , crystalline substances known as Quartz minerals. ELEMENT: A pure substance that cannot be broken down by chemical processes. ATOM: smallest particle of an element that retains its chemical id...

Minerals  MINERALOGY WHAT IS MINERALOGY? It is the study of naturally occurring , crystalline substances known as Quartz minerals. ELEMENT: A pure substance that cannot be broken down by chemical processes. ATOM: smallest particle of an element that retains its chemical identity. Contains protons, neutrons, & electrons.  Elements & Atoms Atoms are composed of smaller particles referred to as: – Protons – Neutrons – Electrons Atomic number (number of protons) determines element. Mass number (protons + neutrons)  ATOMS Stable atoms want positive & negative charges balanced electron shells full Ions- positive (Cations) and negative (Anions) Bonding Ionic Covalent Metallic Van der Waal’s Ionization: addition/subtraction of electrons. CATIONS: positively charged, electrons removed. Al3+, Si4+, Fe2+ or Fe3+ ANIONS: negatively charged, electrons added. O2-, F-, Cl- Anions and cations bound together to form neutral species or minerals. Fig. 02.05 Minerals: the building blocks of rocks  Definition of a Mineral:  naturally occurring  inorganic  homogeneous solid  characteristic crystalline structure  definite chemical composition CHALCEDONY TOURMALIN  MINERALS Natural Occurring biotite Formed by natural processes and not in the laboratory. Is an ice cube a mineral? Is the ice on the wind shield of a car a mineral? orthoclase Minerals manufactured by humans are not minerals. Perfect basal cleavage as seen in biotite (black), and good cleavage seen in the  MINERALS Inorganic  Formed by inorganic processes; not living Minerals are not made from living things  Coal is made of carbon. Is it a mineral? Fluorite and Calcite Azurite and  MINERALS Homogeneous A mineral is a compound that contains the same chemical composition throughout and cannot be physically separated into more than one chemical compound. Pyroxene Tremolite  MINERALS Solid Minerals cannot be a gas or a liquid H2O as ice in a glacier is a mineral, but water is not. Bornite Amethyst  MINERALS Definite Chemical Composition  Minerals should have chemical composition that can be expressed by a chemical formula. Quartz – SiO2 Olivine – (Mg,Fe)2SiO4 Biotite Calcite Barite  MINERALS Highly Ordered Atomic Arrangement  Atoms in a mineral are arranged in an ordered geometric pattern. Gypsum Hornblende  MINERALS This ordered arrangement of atoms is called a crystal structure, and thus all minerals are crystals e.g. Diamond, Quartz. One of the consequences of this ordered internal arrangement of atoms is that all crystals of the same mineral look similar. Amethys Citrine Quartz  External form reflects internal form Minerals’ atoms are regularly arranged Arrangement controls external crystal form Grossular Ca3Al2Si3O12 Mineral photos courtesy J. H. Diamond C Betts Diamond C  The Chemical Composition of Minerals: A mineral always contains certain elements in definite proportions. An element is a substance composed of a single kind of atom. All atoms of the same element have the same chemical and physical properties.  continued Chemical Properties Almost all minerals are compounds, where two or more elements are combined to make a new substance. Some minerals are made up of compounds, and some minerals are made up of pure elements (or atoms of one kind). Elements such as copper, silver and gold are considered minerals. Ore Mineral MINERALS A mineral or an aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined or extracted. Gangue Minerals The unwanted minerals with which ore minerals are usually intergrown. Gold with quartz Chalcopyrite and  MINERALS Industrial Mineral Any naturally-occurring rock or mineral of economic value, exclusive of metallic ores, mineral fuels, and gem stones. Ex: barite, gypsum, talc, silica etc Strategic Mineral A mineral that would be needed to supply the military, industrial, and essential civilian needs of a country during a national emergency. Ex: manganese, platinum, bauxite, chromite (chromium) etc. Argentite: Ore Ag S minerals 2 Arsenopyrite FeAsS Bornite Cu5FeS4 Cassiterite SnO2 Chalcocite Cu2S Chalcopyrite CuFeS2 Chromite (Fe, Mg)Cr2O4 Cinnabar Hg S Cobaltite (Co, Fe)AsS Covellite CuS Enargite Cu3AsS4  Ore minerals Galena: PbS Gold: Au Hematite: Fe2O3 Ilmenite: FeTiO3 Magnetite: Fe3O4 Malachite: Cu2CO3(OH)2 Molybdenite: MoS2  Ore minerals Pentlandite: (Fe, Ni)9S8 Pyrolusite: MnO2 Scheelite: CaWO4 Sphalerite: ZnS Uraninite : UO2 Wolframite: (Fe, Mn)WO4 Mineral Identification Basics PHYSICAL PROPERTIES OF CRYSTALS A CRYSTAL is the outward form of the internal structure of the mineral. The 6 basic crystal systems are: (*) ISOMETRIC HEXAGONAL TETRAGONAL ORTHORHOMBIC Drusy Quartz on Barite MONOCLINIC TRICLINIC (*) Mineral Identification Basics PHYSICAL PROPERTIES CRYSTALS The first group is the ISOMETRIC. This literally means “equal measure” and refers to the equal size of the crystal axes. (*) ISOMETRIC - Fluorite Crystals Mineral Identification Basics ISOMETRIC CRYSTALS a3 ISOMETRIC In this crystal system there are 3 axes. Each has the same length as indicated by a2 the same letter “a”. They all meet at mutual 90o angles in the center of the crystal. a1 Crystals in this system are typically blocky or ball-like. (*) ISOMETRIC Basic Cube Mineral Identification Basics ISOMETRIC CRYSTALS a3 a3 a1 a2 a2 a1 Fluorite cube with crystal axes. (*) ISOMETRIC - Basic Cube (*) Mineral Identification Basics ISOMETRIC BASIC CRYSTAL SHAPES Spinel Fluorite Pyrite Octahedron Cube Cube with Pyritohedron Striations These are all examples of Garnet ISOMETRIC Minerals. Garnet - Dodecahedron Trapezohedron (*) Mineral Identification Basics HEXAGONAL CRYSTALS c a3 a2 a1 HEXAGONAL - Three horizontal axes meeting at HEXAGONAL Crystal angles of 120o and one Axes perpendicular axis. (*) Mineral Identification Basics HEXAGONAL CRYSTAL These hexagonal CALCITE crystals nicely show the six sided prisms as well as the basal pinacoid. (*) (*) Mineral Identification Basics TETRAGONAL CRYSTALS c TETRAGONAL Two equal, horizontal, mutually perpendicular axes (a1, a2) (*) Vertical axis (c) is perpendicular to the a2 horizontal axes and is of a different length. (*) a1 c TETRAGONAL Crystal a2 a1 Axes This is an Alternative Crystal Axes (*) Mineral Identification Basics TETRAGONAL CRYSTALS WULFENITE Same crystal seen edge on. (*) Mineral Identification Basics ORTHORHOMBIC CRYSTALS ORTHORHOMBIC Three mutually perpendicular axes c of different lengths. (*) b c a b a ORTHORHMOBIC An Alternative Crystal Axes Crystal Axes Orientation (*) Mineral Identification Basics ORTHORHOMBIC CRYSTALS Topaz from Topaz Mountain, Utah. (*)  Mineral Identification Basics ORTHORHOMBIC CRYSTALS C axis C axis B axis B axis A axis A axis The view above is looking down the “c” axis of the crystal. (*) BARITE is also orthorhombic. (*) (*) Mineral Identification Basics ORTHORHOMBIC CRYSTALS Pinacoid View (*) This is a Staurolite TWIN with garnets attached. (*) STAUROLITE (*) STAUROLITE Prism View (*) Mineral Identification Basics MONOCLINIC CRYSTALS MONOCLINIC In this crystal form the axes c are of unequal length. (*) Axes a and b are perpendicular. (*) b Axes b and c are perpendicular. (*) a But a and c make some oblique angle and with each other. (*) MONOCLINIC Crystal Axes Mineral Identification Basics MONOCLINIC CRYSTALS Gypsum Mica Top View (*) Orthoclase Mineral Identification Basics TRICLINIC CRYSTALS c TRICLINIC In this system, all of the axes are of different a b lengths and none are perpendicular to any of TRICLINIC Crystal the others. (*) Axes Mineral Identification Basics TRICLINIC CRYSTALS Microcline, variety Amazonite (*) END OF LECTURE Minerals: the building blocks of rocks  Definition of a Mineral:  naturally occurring  inorganic  homogeneous solid  characteristic crystalline structure  definite chemical composition CHALCEDON TOURMALIN  Minerals Minerals may be subdivided into two majors groups: SILICATES NON-SILICATES  Minerals Silicates are by far the most abundant mineral group accounting for more than 90% of the Earth's crust.  Silicates are the major rock-forming minerals. It follows that oxygen and silicon are the most abundant elements in the crust.  Mineral Groups  Silicates (most abundant)  Non-silicates (~8% of Earth’s crust): – Oxides O2- – Carbonates (CO3)2- – Sulfides S2- – Sulfates (SO4)2- – Halides Cl-, F-, Br- – Native elements (single elements; e.g., Au)  Minerals The basic building block of the silicates is the silica tetrahedron. Each silicon atom is attached to four oxygen atoms by tetrahedral bonds. This results in a 4- charge on the SiO4 group. SILICATE MINERALS are subdivided into six subclasses by the degree of polymerization in the chemical structure How tetrahedra may be linked Isolated tetrahedra:(nesosilicates/orthosilicates) Paired silicate tetrahedra: (sorosilicates) Silicate tetrahedra forming rings:(cyclosilicates) Single chain of tetrahedra: (inosilicates) Double chains of tetrahedra: (also inosilicates) Sheets of tetrahedra: (phyllosilicates) 3D framework of tetrahedra: (tectosilicates)  Mineral Groups nesosilicat e – Silicates – inosilicate s tectosilicat es phyllosilicat es Nesosilicates - Isolated Tetrahedra Representativ es: Garnet Kyanite Olivine Tetrahedra does not share any oxygens with neighboring silicon 5. Silicates are the group most important ions mineral Isolated Tetraheda Silicates (Nesosilicates) Tetrahedra do not share any oxygens with neighboring silicon ions Charge balance achieved by bonding with cations e.g., Olivine, Garnet, Kyanite  OLIVINE GROUP Solid solution series MgSiO4- FeSiO4 (Single tetrahedra silicates) Nesosilicate s FORSTERITE FAYALITE Olivine crystals Sorosilicates (Paired Silicates) Pairs of tetrahedra share one oxygen Remaining charge balance achieved by bonding with cations e.g., Epidote  Sorosilicates - Paired Tetrahedra Epidote is the most common example Pairs of tetrahedra share one oxygen 5. Silicates are the most important mineral group  Epidote Group ( Sorosilicate) Epidote group (has both (SiO4)4− and (Si2O7)6−  Epidote Ca2(Al,Fe)3O(SiO4)(Si2O7)(OH) Zoisite- Ca2Al3O(SiO4)(Si2O7)(OH) Clinozoisite Ca2Al3O(SiO4)(Si2O7)(OH) Tanzanite Ca2Al3O(SiO4)(Si2O7)(OH) Allanite Ca(Ce,La,Y,Ca)Al2(Fe2+,Fe3+)O(SiO4)(Si2O7) (OH) Dollaseite (Ce)- CaCeMg2AlSi3O11F(OH)  Cyclosilicates - Rings Beryl (Emerald) Tourmaline Sets of tetrahedra share two oxygens to 5. Silicates are the most important mineral group form a ring Ring Silicates (Cyclosilicates) Sets of tetrahedra share two oxygens to form a ring Remaining charge balance achieved by bonding with  Inosilicates - Chains Single Chains (Pyroxenes) Sets of tetrahedra share two oxygens to 5. Silicates are the most important mineral group form a chain  Single-Chain Silicates (Inosilicates) Sets of tetrahedra share two oxygens to form a chain Remaining charge balance achieved by bonding with cations e.g., pyroxenes Mineral Groups – Silicates Pyroxene Group Ferromagnesian / dark silicates (Fe-Mg) Augite 2-directions of cleavage (at nearly 90 degrees)  PYROXENE GROUP inosilicate s ORTHOPYROXENECLINOPYROXENE Enstatite Clinoenstatite Ferrosilite Clinoferrosilite Diopside Aegirine- augite Augite Jadeite Pigeonite Aegirine Hedenbergite Spodumene CALCIC PYROXENE WOLLASTONITE monoclinic monoclinic monoclinic orthorhombi c SODIC PYROXENE DIOPSIDE- HEDENBERGITE  Inosilicates - Chains Double Chains (Amphiboles) Sets of tetrahedra share oxygens (2 and 3 alternation) to form a chain 5. Silicates are the most important mineral group  Double-Chain Silicates (Inosilicates) Sets of tetrahedra share oxygens (2 and 3 alternation) to form a chain Remaining charge balance achieved by bonding with cations e.g., amphiboles Mineral Groups – Silicates Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg) Hornblende 2-directions of cleavage (not at 90 degrees)  AMPHIBOLE GROUP ANTHOPHYLLIT CUMMINGTONITE TREMOLITE HORNBLENDE ALKALIC E SERIES SERIES SERIES AMPHIBOLE SERIES Anthopylli Kupfferite Tremolite Hornblende Glaucophane te Cummingtoni Actinolite Lamprobolite Riebeckite te Grunerite Nephrite Ferrotremol ite  Phyllosilicates - Sheets Sets of tetrahedra share three oxygens 5. Silicates are the most important mineral to form a sheet group  Sheet Silicates (Phyllosilicates) Sets of tetrahedra share three oxygens to form a sheet Remaining charge balance achieved by bonding with cations e.g., micas  Phyllosilicates - Sheets Si2O5 sheets with layers of Mg(OH)2 or Al(OH)3 Micas Clay minerals Talc Serpentine minerals 5. Silicates are the most important mineral group Mineral Groups – Silicates Mica Group and Clay Minerals light silicates (K, Al)  non-ferromagnesian phyllosilicates Muscovite 1-direction of cleavage  MICA GROUP Musc0vite Biotite Lepidolite Phlogopite  Tectosilicates - Three-Dimensional Networks  Quartz Feldspars Sets of tetrahedra share all 4 oxygens in 3 dimensions to form a 3-D network 5. Silicates are the most important mineral group  Mineral Groups – Silicates Feldspar Group K-feldspar light silicates (K-Na-Ca, Al) Most common mineral group Orthoclase Plagioclase tectosilicates 2-directions of cleavage (at 90 degrees) Ca/Na-feldspar  Feldspar Group Feldspars  A second group of alumino-silicates, tetrahedra form three-dimensional frameworks with Ca, Na and K as the balancing cations. The very abundant feldspar are subdivided in : A) K-Na bearing Alkali Feldspars B) Ca-Na solid-solution series called the Plagioclase Series.  Feldspar Group The K-feldspars or alkali feldspars:  Microcline, (Potassium Potassium rich aluminum silicate)  Orthoclase, (Potassium aluminum silicate)  Sanidine, (Potassium sodium aluminum silicate)  Anorthoclase  ( Sodium aluminum silicate)  Albite  ( Sodium aluminum Sodium rich Calcium silicate) rich  ALKALI FELDSPAR  Potassium –rich members of the series I (Monoclinic) CL NI NO O C  ANORTHOCLASE M Soda rich members of the series ( Triclinic) N I IC ICL TR Potassium and sodium feldspars are not perfectly miscible TRICLINI C  FELDSPAR Mixed crystals between orthoclase and albite represent an important mineral series. At high temp. the series is continuous, but upon slow cooling “exsolution” sets in. Exsolution- homogeneous mixed crystals separate into two solid phases which form an intergrowth.  EXSOLUTION Perthitic texture - Orthoclas e Exsolution Albite lamellae of albite occurring in orthoclase or The light gray streaks in this photomicrograph are plagioclase microcline. ( albite) exsolution lamellae in gray Mineral Groups – Silicates Quartz light silicates (pure SiO2) no cleavage (conchoidal fracture) hard, resistant to weathering Quartz Nesosilicate Inosilicate Phyllosilicate Tectosilicat e GOLDICH STABILITY SERIES FERROMAGNESIAN SILICATES Silicates with iron and/or magnesium in their structure. Most ferromagnesian minerals are dark colored and more dense than non- ferromagnesian silicates. Olivine Pyroxene Amphibole Garnet Biotite  Ferromagnesian/Non-ferromagnesian Silicates FERROMAGNESIAN NON-FERROMAGNESIAN SILICATES SILICATES Silicates with iron Silicate minerals and/or magnesium in without substantial their structure. Most Fe and Mg in their ferromagnesian mnls. are dark colored and crystalline structure. more dense than non- Lighter colored. ferromagnesian silicates.  Plagioclase feldspar Olivine  Potassium Feldspar Pyroxene Amphibole  Quartz Garnet  Muscovite Biotite  NON –SILICATE MINERALS Usually form at low temperatures Carbonates Calcite - Ca CO3 Dolomite - CaMg(CO3)2 Evaporite Minerals Gypsum - CaSO -2H O 4 2 Halite - NaCl Oxides Hematite  END OF LECTURE  MINERALOGY Study of naturally occurring crystalline substances (minerals) Definition of Terms Crystal – a homogenous solid possessing long-range, three dimensional, internal order. Mineral – a naturally occurring homogenous solid, with definite chemical composition and an ordered atomic arrangement. It is usually formed by inorganic processes. Rock – is an aggregate of minerals. It can be composed of only one kind of mineral (monomineralic) or of different kinds of minerals. Ore Minerals – those minerals from which one or more metals may be extracted at a profit. Industrial Minerals – those minerals which are, themselves, used for one or more industrial purposes such as in the manufacture of electrical and thermal insulators, refractories, ceramics, glass, abrasives, fertilizers, fluxes, cement, and other building materials. Gems – those minerals which have ornamental value, and which possess the qualities of beauty, durability, rarity, fashionability and portability. INTRODUCTION TO CRYSTALLOGRAPHY AND MINERAL CRYSTAL SYSTEMS Steno’s Law – Constancy of Interfacial Angles Nicholas Steno, a Danish physician and natural scientist, found that, by examination of numerous specimens of the same mineral, when measured at the same temperature, the angles between similar crystal faces remain constant regardless of the size or shape of the crystal. The Six Crystal Systems 1. Isometric – (cubic) the three crystallographic axes are all equal in length and intersect at right angles (90o) to each other c a=b=c;α=β=γ=90˚ a b 2. Tetragonal – Three axes, all at right angles, two of which are equal in length (a and b) and one (c) which is different in length. a=b≠c;α=β=γ=90˚ C b a 3. Orthorhombic – Three axes, all at right angles, and all three of different lengths. C a≠b≠c;α=β=γ=90˚ a b 4. Hexagonal – Four axes. Three of the axes fall in the same plane and intersect at the axial cross at 120˚ between the positive ends. These three axes, labeled a1, a2, and a3 are of the same length. The fourth axis, termed c, may be longer or shorter than the axes set. The c axis also passes through the intersection of the axes set at right angle to the plane formed by the a set. Rhombohedral a=b=c ; α=β=γ=90˚ c a=b≠c;α=β=90˚;γ=120 a3 a2 a1 5. Monoclinic – Three axes, all unequal in length, two of which (a and c) intersect at an oblique angle (not 90°), the third axis (b) is perpendicular to the other two axes. c a≠b≠c; γ≠α=β=90˚ b a 6. Triclinic – The three axes are all equal in length and intersect at three different angles ( any angle but 90°). c a≠b≠c; α≠β≠γ90˚ b a  WHAT IS A MINERAL? A Mineral is a naturally occurring, homogenous solid with a definite, but generally not fixed chemical composition and an ordered atomic arrangement. It is usually formed by inorganic processes. Naturally occurring - formed by a natural process - synthetic products or those produced in the laboratory are not considered minerals example: synthetic ruby is not a mineral Homogenous solid - consists of a single solid substance that cannot be physically subdivided into simpler chemical compounds - excludes gases and liquids - ex. Ice in glacier is a mineral but water is not; liquid mercury fall under mineraloids. Definite chemical composition - means that atoms, or groups of atoms must occur in specific ratios. For ionic crystals (i.e. most minerals) ratios of cations to anions will be constrained by charged balance, however, atoms of similar charge and ionic radius may substitute freely for one another, hence definite, but not fixed.  Not fixed. Ex. Dolomite Ca Mg (CO3)2 is not always pure. It may contain Fe and Mn in place of Mg, therefore chemical formula becomes Ca (Mg,Fe,Mn) (CO3)2.  Ordered atomic arrangement - means crystalline, with three-dimensional periodic arrays of precise geometric arrangement of atoms. -example: both quartz and glass are composed of element Si silicon and O oxygen. The former has a specific arrangement while the latter have random arrangement. Glass lacks consistent atomic order and therefore considered as noncrystalline or amorphous. Another example is graphite and diamond. (Polymorphs-same chem. comp. but have different structures)  Formed by inorganic process - excludes the organically produced compounds - ex. Calcium carbonate in shells, pearl, petroleum and coal - inorganic means pertaining or relating to compound that contains no carbon.  Tectosilicates (Framework Silicates) The tectosilicates or framework silicates have a structure wherein all of the 4 oxygens of SiO4-4 tetrahedra are shared with other tetrahedra. The ratios of Si to O is thus 1:2. Since the Si - O bonds are strong covalent bonds and since the structure is interlocking, the tectosilicate minerals tend to have a high hardness. SiO2 Minerals There are nine known polymorphs of SiO2, one of which does not occur naturally. These are: Refractive Density Name Crystal System Index (g/cm3) (mean) Stishovite Tetragonal 4.35 1.81 Coesite Monoclinic 3.01 1.59 Low () Quartz Hexagonal 2.65 1.55 High () Quartz Hexagonal 2.53 1.54 Kaetite (synthetic) Tetragonal 2.50 1.52 Low () Tridymite Monoclinic or Orthorhombic 2.26 1.47 High () Tridymite Hexagonal 2.22 1.47 Low () Cristobalite Tetragonal 2.32 1.48 High () Cristobalite Isometric 2.20 1.48 Stishovite and Coesite are high pressure forms of SiO2, and thus have much higher densities and refractive indices than the other polymorphs. Stishovite is the only polymorph where the Si occurs in 6 fold (octahedral) coordination with Oxygen, and this occurs due to the high pressure under which the mineral forms. Both Stishovite and Coesite have been found associated with meteorite impact structures. At low pressure with decreasing temperature, SiO2 polymorphs change from high Cristobalite - Low Cristobalite - High Tridymite - Low Tridymite - High Quartz - Low Quartz. The high to low transformations are all displacive transformations. Since displacive transformations require little rearrangement of the crystal structure and no change in energy, the high () polymorphs do not exist at the surface of the earth, as they will invert to the low () polymorphs as temperature is lowered. Transformations between Cristobalite, Tridymite, and Quartz, however, as well as between the high pressure polymorphs and Quartz, are reconstructive transformations. Since reconstructive transformations require significant structural rearrangement and significant changes in energy, they occur slowly, and the high temperature and high pressure polymorphs can occur as metastable minerals at the Earth's surface. Quartz Quartz is hexagonal and commonly occurs as crystals ranging in size form microscopic to crystals weighing several tons. Where it crystallizes unhindered by other crystals, such as in cavities in rock or in a liquid containing few other crystals, it shows well-developed hexagonal prisms and sometimes showing apparent hexagonal pyramids or dipyramid. When it crystallizes in an environment where growth is inhibited by the surroundings, it rarely show crystal faces. It is also found as microcrystalline masses, such as in the rock chert, and as fibrous masses, such as in chalcedony. As visible crystals, Quartz is one of the more common rock forming minerals. It occurs in siliceous igneous rocks such as volcanic rhyolite and plutonic granitic rocks. It is common in metamorphic rocks at all grades of metamorphism, and is the chief constituent of sand. Because it is highly resistant to chemical weathering, it is found in a wide variety of sedimentary rocks. Several varieties of Quartz can be found, but these are usually only distinguishable in hand specimen. Rock Crystal - clear Quartz in distinct crystals - usually found growing in open cavities in rock. Amethyst - violet colored Quartz, with the color resulting from trace amounts of Fe in the crystal. Rose Quartz - a pink colored variety, that usually does not show crystal faces, the color resulting from trace amounts of Ti+4. Smokey Quartz - a dark colored variety that may be almost black, usually forming well- formed crystals. The color appears to result from trace amounts of Al+3 in the structure. Citrine - a yellow colored variety. Milky Quartz - a white colored variety with the color being due to fluid inclusions. Milky Quartz is common in hydrothermal veins and pegmatites. A fibrous variety of Quartz is called Chalcedony. It is usually brown to gray to translucent with a waxy luster. It is found lining or filling cavities in rock where it was apparently precipitated from an aqueous solution. When it shows bands of color, it is commonly called by the following names: Carnelian - red colored Chalcedony Chrysoprase - apple-green colored as a result of coloration from NiO. Agate - alternating curving layers of Chalcedony with different colors or different porosities. Onyx - alternating layers of Chalcedony of different colors or porosities arranged in parallel planes. Bloodstone - green Chalcedony containing red spots of jasper (see below). Very fined grained aggregates of cryptocrystalline quartz makes up rock like Flint and Chert. Flint occurs as nodules in limestone, whereas chert is a layered rock deposited on the ocean floor. The red variety of flint is called Jasper, where the color results from inclusions of hematite.  SILICATE MINERALS Nesosilicates (Island Silicates) If the corner oxygens are not shared with other SiO4-4 tetrahedrons, each tetrahedron will be isolated. Thus, this group is often referred to as the island silicate group. The basic structural unit is then SiO4-4. In this group the oxygens are shared with octahedral groups that contain other cations like Mg+2, Fe+2, or Ca+2. Olivine is a good example: (Mg,Fe)2SiO4. Sorosilicates (Double Island Silicates) If one of the corner oxygens is shared with another tetrahedron, this gives rise to the sorosilicate group. It is often referred to as the double island group because there are two linked tetrahedrons isolated from all other tetrahedrons. In this case, the basic structural unit is Si2O7-6. A good example of a sorosilicate is the mineral hemimorphite - Zn4Si2O7(OH).H2O. Some sorosilicates are a combination of single and double islands, like in epidote - Ca2(Fe+3,Al)Al2(SiO4)(Si2O7)(OH). Cyclosilicates (Ring Silicates) If two of the oxygens are shared and the structure is arranged in a ring, such as that shown here, we get the basic structural unit of the cyclosilcates or ring silicates. Shown here is a six membered ring forming the structural group Si6O18-12. Three membered rings, Si3O9-6, four membered rings, Si4O12-8, and five membered rings Si5O15-10 are also possible. A good example of a cyclosilicate is the mineral Beryl - Be3Al2Si6O18. Inosilicates (Single Chain Silicates) If two of the oxygens are shared in a way to make long single chains of linked SiO4 tetrahedra, we get the single chain silicates or inosilicates. In this case the basic structural unit is Si2O6-4 or SiO3-2. This group is the basis for the pyroxene group of minerals, like the orthopyroxenes (Mg,Fe)SiO3 or the clinopyroxenes Ca(Mg,Fe)Si2O6. 1 Inosilicates (Double Chain Silicates) If two chains are linked together so that each tetrahedral group shares 3 of its oxygens, we can from double chains, with the basic structural group being Si4O11-6. The amphibole group of minerals are double chain silicates, for example the tremolite - ferroactinolite series - Ca2(Mg,Fe)5Si8O22(OH)2. Phyllosilicates (Sheet Silicates) If 3 of the oxygens from each tetrahedral group are shared such that an infinite sheet of SiO4 tetrahedra are shared we get the basis for the phyllosilicates or sheet silicates. In this case the basic structural group is Si2O5-2. The micas, clay minerals, chlorite, talc, and serpentine minerals are all based on this structure. A good example is biotite - K(Mg,Fe)3(AlSi3)O10(OH)2. Note that in this structure, Al is substituting for Si in one of the tetrahedral groups. Tectosilicates (Framework Silicates) If all of the corner oxygens are shared with another SiO4 tetrahedron, then a framework structure develops. The basic structural group then becomes SiO2. The minerals quartz, cristobalite, and tridymite all are based on this structure. If some of the Si+4 ions are replaced by Al+3 then this produces a charge imbalance and allows for other ions to be found coordinated in different arrangements within the framework structure. Thus, the feldspar and feldspathoid minerals are also based on the tectosilicate framework. 2  Mineralogy Definition of a Mineral A mineral is a naturally occurring homogeneous solid with a definite (but not generally fixed) chemical composition and a highly ordered atomic arrangement, usually formed by an inorganic process. Naturally Occurring - Means it forms by itself in nature. Human made minerals are referred to as synthetic minerals. Homogeneous - means that it is a compound that contains the same chemical composition throughout, and cannot by physically separated into more than 1 chemical compound. Solid - means that it not a gas, liquid, or plasma. Definite chemical composition - means that the chemical composition can be expressed by a chemical formula. Examples: o Quartz has the chemical formula SiO2. Whenever we find quartz it consists of Si and O in a ratio of 1 Si to 2 O atoms. o Olivine is an example of a mineral that does not have a fixed chemical composition. In nature we find that Mg and Fe atoms have the same size and charge and therefore can easily substitute for one another in a mineral. Thus, olivine can have the chemical formula Mg2SiO4 or Fe2SiO4 or anything in between. This is usually expressed with a formula indicating the possible substitution - (Mg,Fe)2SiO4. Highly ordered atomic arrangement - means that the atoms in a mineral are arranged in an ordered geometric pattern. This ordered arrangement of atoms is called a crystal structure, and thus all minerals are crystals. For each mineral has a crystal structure that will always be found for that mineral, i.e. every crystal of quartz will have the same ordered internal arrangement of atoms. If the crystal structure is different, then we give the mineral a different name. A solid compound that meets the other criteria, but has not definite crystal structure is a said to be amorphous. One of the consequences of this ordered internal arrangement of atoms is that all crystals of the same mineral look similar. This was discovered by Nicolas Steno in 1669 and is expressed as Steno's Law of constancy of interfacial angles - angles between corresponding crystal faces of the same mineral have the same angle. This is true even if the crystals are distorted as illustrated by the cross-sections through 3 quartz crystals shown below. Another consequence is that since the ordered arrangement of atoms shows symmetry, perfectly formed crystals also show a symmetrical arrangement of crystal faces, since the location of the faces is controlled by the arrangement of atoms in the crystal structure. Usually formed by an inorganic process - The traditional definition of a mineral excluded those compounds formed by organic processes, but this eliminates a large number of minerals that are formed by living organisms, in particular many of the carbonate and phosphate minerals that make up the shells and bones of living organisms. Thus, a better definition appends "usually" to the formed by inorganic processes. The best definition, however, should probably make no restrictions on how the mineral forms. A mineral should not be formed by organic processes. An organic molecule is a molecule that includes at least one carbon atom and at least one hydrogen atom in the molecule The Earth is composed of rocks. Rocks are aggregates of minerals. So minerals are the basic building blocks of the Earth. Currently there are over 4,000 different minerals known and dozens of new minerals are discovered each year. Our society depends on minerals as sources of metals, like Iron (Fe), Copper (Cu), Gold (Au), Silver (Ag), Zinc (Zn), Nickel (Ni), and Aluminum (Al), etc., and non-metals such as gypsum, limestone, halite, clay, and talc. Many minerals of of great economic importance and their distribution, extraction, and availability have played an important role in history. Minerals are composed of atoms. We'll start our discussion with the geological definition of a Mineral. Definition of a Mineral: A mineral is  Naturally formed - it forms in nature on its own (some say without the aid of humans]  Solid ( it cannot be a liquid or a gas)  With a definite chemical composition (every time we see the same mineral it has the same chemical composition that can be expressed by a chemical formula).  and a characteristic crystalline structure (atoms are arranged within the mineral in a specific ordered manner).  usually inorganic, although a mineral can be formed by an organic process. A mineraloid is a substance that satisfies some, but not all of the parts of the definition. For example, opal, does not have a characteristic crystalline structure, so it is considered a mineraloid. Note also that the "minerals" as used in the nutritional sense are not minerals as defined geologically. 1 Examples  Glass - can be naturally formed (volcanic glass called obsidian), is a solid, its chemical composition, however, is not always the same, and it does not have a crystalline structure. Thus, glass is not a mineral.  Ice - is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula H2O, and does have a definite crystalline structure when solid. Thus, ice is a mineral, but liquid water is not (since it is not solid).  Halite (salt) - is naturally formed, is solid, does have a definite chemical composition that can be expressed by the formula NaCl, and does have a definite crystalline structure. Thus halite is a mineral. Atoms Since minerals (in fact all matter) are made up of atoms, we must first review atoms. Atoms make up the chemical elements. Each chemical element has nearly identical atoms. An atom is composed of three different particles:  Protons -- positively charged, reside in the center of the atom called the nucleus  Electrons -- negatively charged, orbit in a cloud around nucleus  Neutrons -- no charge, reside in the nucleus. Each element has the same number of protons and the same number of electrons.  Number of protons = Number of electrons.  Number of protons = atomic number.  Number of protons + Number of neutrons = atomic weight. Isotopes are atoms of the same element with differing numbers of neutrons. i.e. the number of neutrons may vary within atoms of the same element. Some isotopes are unstable which results in radioactivity. 2   Example: o K (potassium) has 19 protons. Every atom of K has 19 protons. Atomic number of K = 19. Some atoms of K have 20 neutrons, others have 21, and others have 22. Thus atomic weight of K can be 39, 40, or 41. 40K is radioactive and decays to 40Ar and 40Ca. Structure of Atoms Electrons orbit around the nucleus in different shells, A Stable electronic configuration for an atom is one 8 electrons in outer shell Thus, atoms often loose electrons or gain electrons to obtain stable configuration. Noble gases have completely filled outer shells, so they are stable. Examples He, Ne, Ar, Kr, Xe, Rn. Others like Na, K loose an electron. This causes the charge balance to become unequal. and produce charged atoms called ions. Positively charged atoms are called cations. Elements like F, Cl, O gain electrons to become negatively charged. Negatively charged ions are called anions. The drive to attain a stable electronic configuration in the outermost shell along with the fact that this sometimes produces oppositely charged ions, results in the binding of atoms together. When atoms become attached to one another, we say that they are bonded together. Crystal Structure All minerals, by definition are also crystals. Packing of atoms in a crystal structure requires an orderly and repeated atomic arrangement. Such an orderly arrangement needs to fill space efficiently and keep a charge balance. Since the size of atoms depends largely on the number of electrons, atoms of different elements have different sizes. Example of NaCl : 3 For each Na atom there is one Cl atom. Each Na is surrounded by Cl and each Cl is surrounded by Na. The charge on each Cl is -1 and the charge on each Na is +1 to give a charged balanced crystal. The structure of minerals is often seen in the shape of crystals. The law of constancy of interfacial angles --- Angles between the same faces on crystals of the same substance are equal. This is a reflection of ordered crystal structure (See figure 5.5 in the textbook). Crystal structure can be determined by the use of X-rays. A beam of X-rays can penetrate crystals but is deflected by the atoms that make up the crystals. The image produced and collected on film, can be used to determine the struture. The method is know as X-ray diffraction. Crystal structure depends on the conditions under which the mineral forms. Polymorphs are minerals with the same chemical composition but different crystal structures. The conditions are such things as temperature (T) and pressure (P), because these effect ionic radii. At high T atoms vibrate more, and thus distances between them get larger. Crystal structure changes to accommodate the larger atoms. At even higher T substances changes to liquid and eventually to gas. Liquids and gases do not have an ordered crystal structure and are not minerals. Increase in P pushes atoms closer together. This makes for a more densely packed crystal structure. Examples: 4   The compound Al2SiO5 has three different polymorphs that depend on the temperature and pressure at which the mineral forms. At high P the stable form of Al2SiO5 is kyanite, at low P the stable from is andalusite, and at high T it is sillimanite.  Carbon (C) has two different polymorphs. At low T and P pure carbon is the mineral graphite, (pencil lead), a very soft mineral. At higher T and P the stable form is diamond, the hardest natural substance known. In the diagram, the geothermal gradient ( how temperature varies with depth or pressure in the Earth) is superimposed on the stability fields of Carbon. Thus we know that when we find diamond it came from someplace in the Earth where the temperature is greater than 1500oC and the pressure is higher than 50,000 atmospheres (equivalent to a depth of about 170 km). 5  Ionic Substitution (Solid Solution) Ionic substitution - (also called solid solution), occurs because some elements (ions) have the same size and charge, and can thus substitute for one another in a crystal structure. Examples:  Olivines Fe2SiO4 and Mg2SiO4. Fe+2 and Mg+2 are about the same size, thus they can substitute for one another in the crystal structure and olivine thus can have a range of compositions expressed as the formula (Mg,Fe)2SiO4.  Alkali Feldspars: KAlSi3O8 (orthoclase) and NaAlSi3O8, (albite) K+1 can substitute for Na+1  Plagioclase Feldspars: NaAlSi3O8 (albite) and CaAl2Si2O8 (anorthite) NaS+5 can substitutes for CaAl+5 (a complex solid solution). Composition of Minerals The variety of minerals we see depend on the chemical elements available to form them. In the Earth's crust the most abundant elements are as follows: 1. O, Oxygen 45.2% by weight 2. Si, Silicon 27.2% 3. Al, Aluminum 8.0% 4. Fe, Iron 5.8% 5. Ca, Calcium 5.1% 6. Mg, Magnesium 2.8% 7. Na, Sodium 2.3% 8. K, Potassium 1.7% 9. Ti ,Titanium 0.9% 10. H, Hydrogen 0.14% 11. Mn, Manganese 0.1% 12. P, Phosphorous 0.1% Note that Carbon (one of the most abundant elements in life) is not among the top 12. Because of the limited number of elements present in the Earth's crust there are only about 4000 minerals known. Only about 50of these minerals are common. The most common minerals are those based on Si and O: the Silicates. Silicates are based on 6 SiO4 tetrahedron. 4 Oxygens covalently bonded to one silicon atom 7