Mineralogy Geol432 & Mineral Optics
Mineral List
Silicates
Phyllo-silicates (Sheet silicates)
TO Layer Silicates Group (serpentine and clay mineral group)
kaolinite serpentine Al2Si2O5(OH)4 Mg3Si2O5(OH)4
TOT Layer Silicates Group (clay mineral group)
pyrophyllite talc Al2Si4O10(OH)2 Mg3Si4O10(OH)2
TOT + Cation Layer Silicates Group (mica group)
biotite lepidolite* muscovite phlogopite K(Mg,Fe)3(AlSi3O10)(OH)2 K(Li,Al)3(AlSi3O10)(F,OH)2 KAl2(AlSi3O10)(OH)2 KMg3(AlSi3O10)(OH)2
TOT + O Layer Silicates Group (chlorite group)
chlorite (Mg,Al,Fe)3(Si,Al)4O10(OH)2(Mg,Al,Fe)3(OH)6
Li
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The Mineral KAOLINITE
Chemistry: Al2 Si2 O5 (OH) 4 , Aluminum Silicate Hydroxide Class: Silicates Subclass: phyllosilicates Groups: The Clays and The Kaolinite Group. Uses: In the production of ceramics, as a filler for paint, rubber and plastics and the largest use is in the paper industry to produce a glossy paper such as is used in most magazines. Specimens Kaolinite, which is named for its type locality, Kao-Ling, Jianxi, China; is a common phyllosilicate mineral. It lends it name to the Kaolinite Group, members of which also belong to the larger general group known as the Clays. Kaolinite's structure is composed of silicate sheets (Si2 O5 ) bonded to aluminum oxide/hydroxide layers (Al2 (OH) 4 ) called gibbsite layers. Gibbsite is an aluminum oxide mineral that has the same structure as these aluminum layers in kaolinite. The silicate and gibbsite layers are tightly bonded together with only weak bonding existing between these silicate/gibbsite paired layers (called s-g layers). The weak bonds between these s-g layers causes the cleavage and softness of this mineral. The structure is very similar to the Serpentine Group and at times the two groups are combined into a Kaoliniteserpentine Group. Kaolinite shares the same chemistry as the minerals halloysite, dickite and nacrite. The four minerals are polymorphs; meaning they have the same chemistry, but different structures. All four minerals form from the alteration (mostly weathering) of aluminum rich silicate minerals such as feldspars. Kaolinite is by far the most common and most clay deposits contain at least some kaolinite. In fact, clay deposits will frequently be nearly 100% kaolinite pure! Kaolinite is important to the production of ceramics and porcelain. It is also used as a filler for paint, rubber and plastics since it is relatively inert and is long lasting. But the greatest demand for kaolinite is in the paper industry to produce a glossy paper such as is used in most magazines.
PHYSICAL CHARACTERISTICS:
Color is usually white, colorless, greenish or yellow. Luster is earthy. Transparency: Crystals are translucent. Crystal System is triclinic; 1. Crystal Habits include foliated and earthy masses. Crystals of any size are quite rare, usually microscopic. Cleavage is perfect in one direction, basal. Fracture is earthy. Hardness is 1.5 - 2 (can leave marks on paper). Specific Gravity is 2.6 (average). Streak is white. Other Characteristics: Clay like properties when water is added. Associated Minerals include fluorite, microcline, pyrite, hemimorphite, augite, dickite, halloysite, montmorillonite, quartz, muscovite and other
clays. Notable Occurrences are spread around the world including the type locality of Kao-Ling, Jianxi, China as well as Cornwall and Devon, England; Haute-Vienne, France; Near Dresden, Saxony, Germany; Donets Basin, Ukraine; Huberdeau, Quebec, and near Walton, Nova Scotia, Canada and in the United States at Macon, Georgia; Dixie Clay Company Mine, South Carolina; near Webster, North Carolina; Arkansas; Mesa Alta, New Mexico and Sterling Hill, New Jersey. Best Field Indicators are habit, softness, color, luster and clay like properties.
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THE MINERAL SERPENTINE
Chemistry: (Mg,Fe)3 Si2 O5 (OH) 4 , Magnesium Iron Silicate Hydroxide Class: Silicates Subclass: phyllosilicates Group: Kalolinite-Serpentine Uses: many industrial applications, including brake linings and fireproof fabrics and as an ornamental stone. Specimens Serpentine is a major rock forming mineral and is found as a constituent in many metamorphic and weather igneous rocks. It often colors many of these rocks to a green color and most rocks that have a green color probably have serpentine in some amount. Serpentine is actually a general name applied to several members of a polymorphic group. These minerals have essentially the same chemistry but different structures. The following is a list of these minerals, their formulas and symmetry class: Antigorite; (Mg,Fe)3 Si 2 O5 (OH) 4 ; monoclinic. Clinochrysotile; Mg 3 Si 2 O5 (OH) 4 ; monoclinic. Lizardite; Mg 3 Si 2 O5 (OH) 4 ; trigonal and hexagonal. Orthochrysotile; Mg 3 Si 2 O5 (OH) 4 ; orthorhombic. Parachrysotile; (Mg,Fe)3 Si 2 O5 (OH) 4 ; orthorhombic. Their differences are minor and almost indistinguishable in hand samples. However, the chrysotile minerals are more likely to form serpentine asbestos, while antigorite and lizardite form cryptocrystalline masses sometimes with a lamellar or micaceous character. Asbestos had been used for years as a fire retarding cloth and in brake linings. Its links to cancer however has led to the development of alternative materials for these purposes. Serpentine's structure is composed of layers of silicate tetrahedrons linked into sheets. Between the silicate layers are layers of Mg(OH)2 . These Mg(OH)2 layers are found in the mineral brucite and are called brucite layers. How the brucite layers stack with the silicate layers is the main reason for the multiple polymorphs. The stacking is not perfect and has the effect of bending the layers. In most serpentines, the silicate layers and brucite layers are more mixed and produced convoluted sheets. In the asbestos varieties the brucite layers and silicate layers bend into tubes that produce the fibers. Serpentine can be an attractive green stone that takes a nice polish and is suitable for carving. It has been used as a substitute for jade and is sometimes difficult to
distinguish from jade, a testament to the beauty of finer serpentine material. Non-fiberous serpentine is not a cancer concern. Asbestos serpentines should be kept in closed clear containers, but makes an attractive specimen. Sometimes with a golden color as the name chrysotile in greek means golden fibers.
PHYSICAL CHARACTERISTICS:
Color is olive green, yellow or golden, brown, or black. Luster is greasy, waxy or silky. Transparency crystals are translucent and masses are opaque. Crystal System is variable, see above. Crystal Habits: never in large individual crystals, usually compact masses or fibrous. Veins of viberous serpentine can be found inside of massive serpentine or other rocks. Cleavage the varieties of crysotile have none, in lizardite and antigorite it is good in one direction. Fracture is conchoidal in antigorite and lizardite and splintery in the crysotiles. Hardness is 3 - 4.5 Specific Gravity is 2.2 - 2.6 Streak white Associated Minerals include chromite, olivine, garnets, calcite, biotite and talc. Other Characteristics: serpentine in the rough has a silky feel to the touch and fibers are very flexible. Notable Occurances Val Antigorio, Italy; Russia; Rhodesia Switzerland; North Carolina, California, Rhode Island and Arizona, USA and Quebec, Canada. Best Field Indicators softness, color, silky feel and luster, asbestos if present and its flexibility.
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THE MINERAL TALC
Chemistry: Mg 3 Si4 O10 (OH) 2 , Magnesium Silicate Hydroxide Class: Silicates Subclass: phyllosilicates Group: Clays and also The Montmorillonite/Smectite Group. Uses: an ornamental and heat, acid and electrically-resistant stone (soapstone) used as counter tops, electrical switchboards, carvings, etc, used as an ingredient in paints, rubber, roofing materials, ceramics and insecticides. Most commonly known as the primary ingredient in talcum powder. Specimens Talc is an important industrial mineral. Its resistance to heat, electricity and acids make it an ideal surface for lab counter tops and electrical switchboards. It is also an important filler material for paints, rubber and insecticides. Even with all these uses, most people only know talc as the primary ingredient in talcum powder. Mineral specimens are not very common as it does not form very large crystals. However, it often replaces other minerals on an atom by atom basis and forms what are called pseudomorphs (false shape). The talc takes the form of the mineral it replaces. A specimen of what looks like milky quartz is quite a suprise when it not only has a soapy feel but can be scratched by a fingernail.
PHYSICAL CHARACTERISTICS:
Color is green, gray and white to almost silver. Luster is dull to pearly or greasy. Transparency crystals are translucent and masses are opaque. Crystal System is monoclinic; 2/m. Crystal Habits: never in large individual crystals, but if found are flattened tabular crystals with a hexagonal cross-section, usually talc is found in compact or lamellar masses. Forms pseudomorphs (false shape) of other crystals such as quartz, pyroxenes, olivine and amphiboles. Cleavage is perfect in one direction, basal. Fracture is uneven to lamellar. Hardness is 1 (can leave mark on paper) Specific Gravity is 2.7 - 2.8 (average) Streak is white. Other Characteristics: cleavage flakes are slightly flexible but not elastic and talc has a soapy feel to the touch. Associated Minerals include serpentine, dolomite, magnesite, quartz, pyroxenes, olivine, biotite and amphiboles.
Notable Occurances: include many mines up and down the Appalachian Mountains and in California and Texas, USA; Florence, Germany; Italy; Tyrol, Austria; Transvaal, South Africa and Shetland, Scotland. Best Field Indicators softness, color, soapy feel, luster and cleavage.
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THE MINERAL BIOTITE
Chemistry: K (Fe, Mg) 3 AlSi3 O10 (F, OH)2 , Potassium iron magnesium aluminum silicate hydroxide fluoride. Class: Silicates Subclass: Phyllosilicates Group: Micas Uses: heat insulator for industrial purposes. Specimens Biotite is a common rock forming mineral, being present in at least some percentage in most igneous and both regional and contact metamorphic rocks. The typical black to brown color of biotite is characteristic although it is difficult to distinguish brown biotite from dark brown phlogopite. The two are actually end members in a series that is dependent on the percentage of iron. Phlogopite is iron poor and biotite is iron rich. The darker color and density increase with an increase in the iron content. Biotite tends to form in a wider range of conditions than phlogopite which is limited mostly to ultramafic rocks and magnesium rich marbles and pegmatites. Biotite, like other micas, has a layered structure of iron magnesium aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage. Biotite is rarely considered a valuable mineral specimen, but it can accompany other minerals and compliment them. In Bancroft, Ontario Biotite forms large crystals with green apatite and hornblende. Single large plates or "books" of biotite can grow to considerable size and can make impressive mineral specimens. Weathered tiny crystals of biotite can appear golden yellow with a nice sparkle producing a "fool's Gold" that has fooled many.
PHYSICAL CHARACTERISTICS:
Color is black to brown and yellow with weathering. Luster is vitreous to pearly. Transparency crystals are transparent to translucent. Crystal System is monoclinic; 2/m Crystal Habits include tabular to prismatic crystals with a prominant pinacoid termination. Biotite's four prism faces and two pinacoid faces form pseudohexagonal crystal "books". The sides of the crystal often tend to tapper and can have a "hard candy that has been sucked on, look". Also as lamellar or granular rock forming masses providing the luster for most schists and gneiss. Cleavage is perfect in one direction producing thin sheets or flakes. Fracture is not readily observed due to cleavage but is uneven. Hardness is 2.5. Specific Gravity is approximately 2.9 - 3.4+ (slightly above average) Streak is white. Associated Minerals are quartz, feldspars, apatite, calcite, hornblende,
garnets and schorl. Other Characteristics: cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape. Notable Occurrences include Bancroft and sudbury, Ontario; Sicily; Russia and many other locallities around the world. Best Field Indicators are crystal habit, color, cleavage, elastic sheets and associations.
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THE MINERAL MUSCOVITE
Chemistry: KAl 2 (AlSi 3 O10 )(F, OH)2 , Potassium aluminum silicate hydroxide fluoride. Class: Silicates Subclass: Phyllosilicates Group: Micas Uses: heat and electrical insulator for industrial purposes. Specimens Muscovite is a common rock forming mineral and is found in igneous, metamorphic and detrital sedimentary rocks. Muscovite has a layered structure of aluminum silicate sheets weakly bonded together by layers of potassium ions. These potassium ion layers produce the perfect cleavage of muscovite. Although it has such easy cleavage, the cleavage sheets are quite durable and are often found in sands that have undergone much erosion and transport that would have destroyed most other minerals. The sheets of muscovite also have high heat and electrical insulating properties and are used to make many electical components. Muscovite sheets were used for kitchen oven windows before synthetic materials replaced them. Muscovite is not often valuable as a mineral specimen but is often associated with other minerals of extrodinary beauty and value. Some very nice muscovite crystals accompany such valuable minerals as tourmaline, topaz, beryl, almandine and others. A rare twin variety from Brazil forms yellow five pointed stars and is called "Star Muscovite". A deep green variety is called fuchsite and is colored by chromium inpurities.
PHYSICAL CHARACTERISTICS:
Color is white, silver, yellow, green and brown. Luster is vitreous to pearly. Transparency crystals are transparent to translucent. Crystal System is monoclinic; 2/m Crystal Habits include tabular crystals with a prominant pinacoid termination. Muscovites four prism faces form diamond shaped "books" and if modified by another pinacoid they form pseudo-hexagonal crystal "books". The sides of the crystal often tend to tapper. Also as lamellar rock forming masses and small flakes in detrital matterial. Twinned crystals can form flat five pointed stars. Cleavage is perfect in one direction producing thin sheets or flakes. Fracture is not readily observed due to cleavage but is uneven. Hardness is 2 - 2.5. Specific Gravity is approximately 2.8 (average) Streak is white. Associated Minerals are quartz, feldspars, beryl and tourmalines. Other Characteristics: cleavage sheets are flexible and elastic, meaning they can be bent and will flex back to original shape. Notable Occurrences include India, Pakistan, Brazil and many USA locallities. Best Field Indicators are crystal habit, cleavage, elastic sheets, color and associations.
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THE MINERAL CHLORITE
Chem...