Rock Forming Minerals PDF

WARDIERE, INC. HOME ABOUT CONTENT OTHERS ROCK FORMING MINERALS PRESENTED BY: PRINCESS PORTIA AND SHAI LOURECE WARDIERE, INC. HOME ABOUT CONTENT OTHERS OBJECTIVES: In this lesson, you should be able to:...

WARDIERE, INC. HOME ABOUT CONTENT OTHERS ROCK FORMING MINERALS PRESENTED BY: PRINCESS PORTIA AND SHAI LOURECE WARDIERE, INC. HOME ABOUT CONTENT OTHERS OBJECTIVES: In this lesson, you should be able to: identify common rock-forming minerals using their physical and chemical properties; and identify the minerals important to society. WARDIERE, INC. HOME ABOUT CONTENT OTHERS A MINERAL IS A NATURALLY OCCURRING, INORGANIC, HOMOGENEOUS SOLID, WITH A DEFINITE CHEMICAL COMPOSITION, AND AN ORDERED CRYSTALLINE STRUCTURE. MOST MINERALS HAVE DISTINCTIVE CHARACTERISTICS. SOME MINERALS, HOWEVER, ARE VERY SIMILAR THAT THEIR PHYSICAL PROPERTIES SHOULD BE EXAMINED FURTHER TO MAKE A CORRECT IDENTIFICATION.  WARDIERE, INC. HOME ABOUT CONTENT OTHERS PHYSICAL PROPERTIES OF MINERALS THERE ARE SEVERAL LABORATORY AND FIELD TECHNIQUES BEING USED TO DISTINGUISH MINERALS BASED ON PHYSICAL PROPERTIES. SOME MINERALS ARE TOO SMALL TO BE IDENTIFIED BY THE NAKED EYE THAT IS WHY THERE IS A NEED FOR HIGH-POWERED INSTRUMENTS SUCH AS A PETROGRAPHIC MICROSCOPE AND X-RAY DIFFRACTOMETERS (XRDS). ON THE OTHER HAND, THERE ARE MINERALS THAT ARE LARGE ENOUGH TO BE ASSESSED BASED ON THEIR PHYSICAL PROPERTIES. WARDIERE, INC. HOME ABOUT CONTENT OTHERS GEOLOGISTS COMMONLY USE PHYSICAL PROPERTIES SUCH AS COLOR, STREAK, LUSTER, CRYSTAL HABIT, CLEAVAGE, FRACTURE, HARDNESS, AND SPECIFIC GRAVITY TO IDENTIFY MINERALS. COLOR COLOR REFERS TO CERTAIN WAVELENGTHS OF LIGHT THAT ARE REFLECTED BY THE MATERIAL, IN THIS CASE, A MINERAL AND IS PERCEIVED BY THE OBSERVER. IT IS THE MOST NOTICEABLE PHYSICAL PROPERTY OF A MINERAL AND IS OFTEN THE FIRST THING THAT PEOPLE CONSIDER WHEN LOOKING FOR MINERALS AS GEMSTONES FOR JEWELRY. HOWEVER, USING THIS AS SOLE BASIS FOR MINERAL IDENTIFICATION IS NOT ENOUGH BECAUSE DIFFERENT MINERALS CAN HAVE THE SAME COLOR. IN ADDITION, COLOR IS HIGHLY AFFECTED BY IMPURITIES OR LIGHT DIFFRACTION. MINERAL COLORS CAN BE CLASSIFIED INTO IDIOCHROMATIC, ALLOCHROMATIC AND PSEUDOCHROMATIC.  WARDIERE, INC. HOME ABOUT CONTENT OTHERS SELF-COLORED MINERALS ARE CALLED IDIOCHROMATIC MINERALS. THEIR COLOR IS A DIAGNOSTIC PROPERTY. THIS MEANS THAT THE COLOR OF A MINERAL IS CONSTANT AND IT DEPENDS ON THE ELEMENTS THAT MAKE UP THEIR CHEMICAL STRUCTURE. EXAMPLES ARE MALACHITE (ALWAYS GREEN), RHODOCHROSITE (ALWAYS RED) AND SULFUR (ALWAYS YELLOW). FOR ALLOCHROMATIC MINERALS, COLOR IS NOT A RELIABLE DIAGNOSTIC PROPERTY SINCE SMALL IMPURITIES MAY DRAMATICALLY ALTER THEIR COLOR. FOR EXAMPLE, QUARTZ MAY OCCUR IN DIFFERENT VARIETIES. THIS INCLUDES COLORLESS, MILKY, SMOKY, CITRINE, AMETHYST, AND ROSE AS SHOWN BELOW. ALLOCHROMATIC MINERALS ARE OFTEN WEAKLY-COLORED OR COLORLESS IN THEIR PURE STATE, WHICH ALLOWS IMPURITIES TO PERVADE THEM WITH COLOR. BY CONTRAST, IDIOCHROMATIC MINERALS ARE STRONGLY COLORED WHICH DROWNS OUT ANY IMPURITIES IN COLOR. FOR ALLOCHROMATIC MINERALS, COLOR IS NOT A RELIABLE DIAGNOSTIC PROPERTY SINCE SMALL IMPURITIES MAY DRAMATICALLY ALTER THEIR COLOR. FOR EXAMPLE, QUARTZ MAY OCCUR IN DIFFERENT VARIETIES. THIS INCLUDES COLORLESS, MILKY, SMOKY, CITRINE, AMETHYST, AND ROSE AS SHOWN BELOW. ALLOCHROMATIC MINERALS ARE OFTEN WEAKLY-COLORED OR COLORLESS IN THEIR PURE STATE, WHICH ALLOWS IMPURITIES TO PERVADE THEM WITH COLOR. BY CONTRAST, IDIOCHROMATIC MINERALS ARE STRONGLY COLORED WHICH DROWNS OUT ANY IMPURITIES IN COLOR. LASTLY, PSEUDOCHROMATIC MINERALS ARE FALSE-COLORED MINERALS. THEIR COLORS ARE DUE TO LIGHT DIFFRACTION. IN THIS INSTANCE, COLOR MAY BE VARIABLE BUT IS AN EXCLUSIVE PROPERTIES OF THE MINERAL. STREAK THE STREAK IS THE COLOR OF THE POWDERED FORM OF A MINERAL. IT IS OBSERVED BY RUBBING THE MINERAL ACROSS A STREAK PLATE. AS SHOWN BELOW, THE COLOR OF THE MINERAL IS NOT ALWAYS THE SAME AS THE STREAK COLOR. FOR MINERAL IDENTIFICATION, THIS PROPERTY IS MORE RELIABLE THAN THE COLOR OF THE MINERAL SINCE STREAK IS ALWAYS THE SAME. LUSTER LUSTER IS THE APPEARANCE OF A MINERAL'S SURFACE AND IS DEPENDENT ON HOW IT REFLECTS LIGHT. COMMON LUSTER TYPES ARE PEARLY, SILKY, DULL, RESINOUS, EARTHY, ADAMANTINE, VITREOUS OR GLASSY, AND METALLIC. REFER TO THE FIG. 5 AND TABLE 1 FOR THE DESCRIPTION OF EACH TYPE. CRYSTAL HABIT CRYSTAL HABIT IS THE CHARACTERISTIC SHAPE IN WHICH A MINERAL GROWS AND IS A PROJECTION OF THE MINERAL'S CRYSTAL STRUCTURE. SOME COMMON HABITS ARE ACICULAR, BLOCKY, TABULAR, FIBROUS, BLADED, DENDRITIC, AND PRISMATIC AS SHOWN BELOW. REFER TO FIG. 6 AND TABLE 2 FOR THE DESCRIPTION OF EACH TYPE. CLEAVAGE CLEAVAGE IS THE TENDENCY OF SOME MINERALS TO BREAK ALONG FLAT SURFACES. THESE SURFACES HAVE THE WEAKEST ATOMIC BONDING WHICH MEANS THAT WHEN YOU USE A HAMMER TO BREAK A MINERAL, IT WILL ALWAYS BREAK ALONG THISPOINTS. CLEAVAGE SURFACES TEND TO OCCUR REPETITIVELY AS PARALLEL PLANES AT CRYSTAL BREAKS, WHICH CONSTITUTE A SET,OR DIRECTION OF CLEAVAGE. THE ILLUSTRATION BELOW SHOWS SOME OF THE TYPES OF CLEAVAGE PLANES. CLEAVAGE CLEAVAGE IS THE TENDENCY OF SOME MINERALS TO BREAK ALONG FLAT SURFACES. THESE SURFACES HAVE THE WEAKEST ATOMIC BONDING WHICH MEANS THAT WHEN YOU USE A HAMMER TO BREAK A MINERAL, IT WILL ALWAYS BREAK ALONG THISPOINTS. CLEAVAGE SURFACES TEND TO OCCUR REPETITIVELY AS PARALLEL PLANES AT CRYSTAL BREAKS, WHICH CONSTITUTE A SET,OR DIRECTION OF CLEAVAGE. THE ILLUSTRATION BELOW SHOWS SOME OF THE TYPES OF CLEAVAGE PLANES.  Fracture Fracture is the pattern in which the mineral breaks aside from its planes of cleavage. This happens when the atomic bonds are of equal strength. Unlike cleavage, fracture does not break along planes; it just breaks unevenly. Various types of fractures exist in nature such as conchoidal, jagged, uneven and splintery.  HARDNESS Hardness is the resistance of the minerals to scratching. It is measured by scratching the mineral with another object of known hardness. For more accurate measurement, Mohs scale of hardness is used which is composed of ten minerals, numbered from 1 to 10 (1 as the softest and 10 as the hardest). The Mohs scale is a relative scale, not qualitative, which means that gypsum (H=2) is not twice as hard as talc (H=1), only that gypsum is harder than talc. The Mohs scale of hardness was named after its proponent, Friedrich Mohs. Mohs was born on January 29, 1773, in Gernrode, Germany. His early studies largely focused on Physics, Chemistry, and Mathematics but later on, he took advanced studies in the mining academy. His interest in mineralogy was inspired by one of his professors named Dr. Werner. In 1801, he became a curator of a private mineral collection owned by a banker named J.F. van der Null. He was required to arrange the minerals into categories, so he started studying the different physical properties of these minerals. He discovered the varying hardness of the minerals and later on designed a systematic classification of this property using a scratch test.  Specific Gravity Specific gravity is the ratio of a minerals' weight to the weight of an equal volume of water. Therefore, a specific gravity of 4 means that a certain substance is four times heavier than water. The size of the mineral is independent of its specific gravity. This means that a larger sample can still yield a smaller specific gravity. The table below shows some of the specific gravity of common minerals. Notice that diamond, the hardest mineral, has a low specific gravity.  Chemical Properties of Minerals All minerals can be represented by a chemical formula, which presents the proportions of atoms that constitute them. For example, the mineral quartz has a chemical formula SiO₂. Its crystal structure is a continuous framework of silicon-oxygen tetrahedra. The chemical properties of minerals depend on their chemical formula and crystal structure. Solubility and melting point are chemical properties commonly used to describe a mineral. Solubility Solubility refers to the ability of a substance to dissolve in a solvent at a specified temperature. For example, biotite, a mineral commonly found in igneous rocks, is soluble in both acid and base solutions. The dissolution releases the loosely-bound potassium ions in the mineral.  The melting point refers to the temperature at which solid turns into liquid. Minerals composed of atoms that are tightly bonded within the crystal structure have high melting points. For example, quartz melts above 1670°C. Mineral Groups Determined by Chemical Composition Thousands of minerals have been identified and in order to study them closely, geologists group them based on their chemical composition. Table 6 shows the nine broad mineral groups and their description.  Analysis of the Composition and Crystal Structure of Minerals In the laboratory, the composition and crystal structure of minerals can be analyzed through chemical and instrumental analysis. Chemical composition is investigated using wet chemical analysis and several spectroscopic techniques. Wet Chemical Analysis The wet chemical analysis involves dissolving a mineral in an acid and analyzing the solution. An acid used is usually hydrochloric acid (5-10%). If a bubble is evident after putting drops of the acid, it indicates that carbonate minerals such as calcite. and dolomite is present. The table below shows the reaction of common carbonate minerals to acids.  Spectroscopic Techniques Spectroscopic techniques involve quantitative analysis of mineral components depending on the light absorbance of the compounds. These test the sample's interactions with electromagnetic radiation to determine its structural and chemical properties. The types of spectroscopic techniques are listed below. 1. Atomic absorption spectroscopy (AAS) uses a controlled flame to separate the components of a sample and monochromator linked to a detector to search for wavelengths of light that are absorbed by the sample. This technique identify the concentration of mineral in a sample. 2. Inductively coupled plasma (ICP) spectroscopy uses argon gas to move the sample vapor into a chamber under high vacuum where both the sample and the gas are heated for the elements to give off a characteristic wavelength of light. This technique is able to trace and identify almost all the minerals present in the sample. 3. X-ray fluorescence (XRF) spectroscopy uses high voltage electrons toward a metal target to produce a specific wavelength X-ray beam that hits the sample. Comparing the sample intensities to that of the standard can be used to calculate the concentration of elements present in the mineral. This technique will give an analyst a real-time rock analysis. This is more convenient and efficient than the older technique which takes weeks before analysis is presented.  4. X-ray diffraction spectroscopy (XRD) is a technique that only applies to pure amorphous or crystalline substances and is used to study the structure of the crystals. This process is done by firing an X-ray beam at a finely-ground sample at different angles. Then reflected or diffracted rays can be used to compute for the dimensions of the unit cell. This technique is used to obtain information from unknown crystalline substances. Common Rock-Forming Minerals The common rock-forming minerals are quartz, feldspar, mica, pyroxene, amphibole, and olivine. All of the following silicate minerals, except for quartz, are mineral groups.  Quartz Quartz has a chemical composition of SiO₂. It is a glass-like hard substance with white streaks. It has Mohs hardness of 7 which makes the quartz grains resist scratching of nail or a pocket knife. Pure quartz is also known as "rock crystal" that is colorless and transparent. Trace amounts of impurities cause colored varieties of quartz. Quartz can occur as amethyst (purple-violet), citrine (yellow), smoky or cairngorm (brown), morion (black), rose (pink), sapphire quartz (blue), and milky (semi-translucent white). The grains of quartz, in general, are irregular in shape and exhibits conchoidal fracture.  Feldspar Feldspar has a chemical composition of XAISIO, where X is potassium (K), calcium. (Ca), or sodium (Na). It is quite hard with a Mohs hardness of 6. It is a light-colored mineral, usually white, but can also exist in lighter shades of red or green. It has a glassy luster. In rocks, feldspar forms rectangular crystals that break along flat faces. 1. Plagioclase feldspar (NaAlSi O or CaAl Si₂O) is the most common mineral in igneous rocks. Most plagioclase appears frosty white to dark gray. Using a hand lens, one can often see the stair- step like cleavage and possible striations or parallel grooves.  2. Potassium feldspar (KAISI₃O₂) commonly occurs as slightly pinkish grains. Unlike plagioclase, it does not contain striations on its cleavage faces. It also has two cleavage planes both at 90°. Mica Mica is any group of hydrous potassium aluminum silicate minerals. Mica is soft, with hardness ranging from 2 to 2.5. It is easily identified by its perfect cleavage, reducing it to thin smooth flakes. Its luster is responsible for the flashes of light in rocks such as granite and slate.  1. Muscovite mica [KAI, AISI O10) (OH)2] occurs as a white, shiny and silvery mineral. It has a pearly to vitreous luster, white streak and often sheds into tiny flakes when scratched. 2. Biotite mica [K₂(Mg,Fe) AlSi3O (OH,O,F)] is black, dark green, or dark brown, shiny, and often occurs in small- hexagonal crystals. It has a vitreous luster, flaky habit and white to gray streak. Biotite sheets are elastic when bent.  Pyroxene Pyroxene minerals have a general composition of XY(AI,Si)₂O, where X is calcium (Ca) or magnesium (Mg) and Y is either magnesium (Mg), iron (Fe), or aluminum (Al). It occurs as short, stubby and black to dark-green crystals (although other colors may occur). It has a glassy luster with streaks of white, light green, or light brown. It has good cleavage in two directions (both at almost 90°) and cleavage surfaces are often hard to see in a regular rock sample. Augite is the most common mineral of this group. Amphibole Amphibole has a general formula of WXYZO(OH), and has a dark color with a Mohs hardness ranging from 5 to 6. It is opaque and has a glassy luster. It occurs as long and slender crystals. It has good cleavage in two directions (approximately 60°and 120") and therefore has al stair-step appearance under a hand lens. Hornblende is the most common amphibole.  Olivine Olivine is a silicate mineral with a general chemical composition of (Mg, Fe) SiO but calcium, manganese, and nickel can be substituted for magnesium and iron. It occurs as small, light green, glassy crystals. It is commonly used in the gemstone industry as peridot. It is a glassy looking and transparent substance that is almost as hard as quartz. Its sugary or sacharroidal texture and olive-green color make it distinctive from other rock-forming minerals. EXAMPLE:  ‼️Key Points‼️ A mineral is a naturally occurring, inorganic, solid material that has a fixed structure and a definite chemical composition, The physical properties of minerals are color, streak, luster, crystal habit, cleavage, fracture, hardness, and specific gravity. These properties are used for mineral identification. Solubility and melting point are chemical properties commonly used to describe a mineral. The most common rock-forming minerals are quartz, feldspar, mica, pyroxene, amphibole, and olivine. WARDIERE, INC. HOME ABOUT CONTENT OTHERS THANK YOU -