70Introduction to MineralsI. Minerals and Basic PropertiesA. Mineral - naturally occurring inorganic solid, consisting of atoms combined together aschemical compounds, possessing a definable internal structure.1. Rocks are composed of 1 or more mineral crystals combined together asaggregates.2. atoms---bonded----compounds/minerals----combined/lithified----rocks-----createstructure of earthB. Physical Properties of Minerals - the unique chemical/atomic composition of minerals andthe crystalline arrangement of the atoms within the mineral structure give a particularmineral a defineable and recognizable set of physical properties.1. Crystal Form of a mineral - the external expression of a mineral that reflects theorderly internal arrangement of atoms. a. E.g. quartz crystals - if a mineral is allowed to form without spacerestrictions, it will develop individual xls with well developed crystal faces. 2. Luster - the appearance or quality of light reflected from the surface of a mineral. a. E.g. metallic luster, submetallic, vs. non-metallic luster (includes glassy,pearly, silky, resinous, and dull)3. Color - colors can be helpful in identifying a mineral, but is generally useful as minorimpurities in a mineral can cause wide color variation (e.g. quartz comes in pink,purple, white, gray)4. Streak - the color of a mineral in its powered form obtained by rubbing it across aporcelain plate. Streak color can be very different from the mineral color.5. Hardness - resistance of a mineral to abrasion or scratching. Very diagnostic of amineral. Mohs hardness scale developed as a frame of reference.6. Cleavage - tendency of of a mineral to break along planes of weak atomic bonding.Different minerals have different types and directions of cleavage.7. Fracture - minerals (e.g. quartz) do not have cleavage but instead break alonguneven surfaces. a. Conchoidal fractrue = breaks like glass. b. Others may break into splinters or irregularly.8. Specific Gravity - Ratio of the weight of a mineral relative to a similar volume ofwater.71a. E.g. if a 1 cm3 piece of mineral weighs 3 x as much as 1 cm3 of water, itss.g. -= 3.C. Mineral Groups (over 2000 minerals types known to exist, only about 24 are mostabundant)1. Rock Forming Minerals - those minerals that are the most abundantly found on theearth and that most commonly comprise rocks. a. 8 Elements constitute 98% of the earth's crustal mineralsoxygen 46.6%Silicon 27.7%Aluminum 8.1%Iron 5.0%Calcium 3.6%Sodium 2.8%Potassium 2.5%Magnesium 2.1%Others 1.5%Total 100%2. Silicates- Most common mineral groups composed of silica and oxygen...known asthe silicates a. composed primarily of silica and oxygen with subordinate amounts of otherelements to maintain electrical neutrality on the subatomic level).3. Carbonates - Ca and CO3 - next common4. Oxides - consist of metallic elements and oxygen5. Native Elements - Au, Ag, and C (diamond).a. e.g. of mineral uses, quartz = glass, calcite = cement, gypsum = plaster.D. Silicate Structures1. Basic Building Block of Silicate Minerals is the silica-oxygen tetrahedron. a. 4 Oxygen atoms surrounding a Si atom in between. The Si-O tetrahedronforms a complex anion with a net negative charge of -4 (Si = +4, 4(O -2) = -8;-8 + 4 = -4) b. thus positively charged metal ions are commonly incorporated into the bondsof Si-tetrahedron to satisfy charge balancing.722. Silica tetrahedra may be linked together to form a. single chainsb. double chainsc. sheet structures3. Silicate Mineralsa. Ferromagnesian Silicates - silicate minerals (compounds containing Si-Otetrahedron) that are linked together and include Fe and Mg. (1) Typically dark in color, high specific gravity, and crystallize frommagma at relatively high temperatures.(2) e.g. Olivine, Pyroxene, Amphibole, Biotite, and Garnet)b. Nonferromagnesian Silicates - silicate minerals that are linked together anddo not include Fe and Mg. (1) Typically lighter in color, less specific gravity, crystallize from magmaat relatively lower temperatures (2) e.g. quartz, feldspars, muscovite, clay)E. Nonsilicate Minerals - minerals that are compounds that do not have silica and oxygen intheir structure 1. carbonates, 2. sulfates, 3. oxides, 4. native elements, 5. halides, 6.
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