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Descriptions of Rock Forming Minerals : All the following minerals are made of silica tetrahedrons, either alone or combined with other elements. Quartz. Quartz (SiO 2 )is silicon dioxide. It has a glassy or greasy luster. 7 on Mohs hardness scale

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Descriptions of Rock Forming Minerals: All the following minerals are made of silica tetrahedrons, either alone or combined with other elements

quartz
Quartz
  • Quartz (SiO2)is silicon dioxide. It has a glassy or greasy luster.
  • 7 on Mohs hardness scale
  • Colour varies froms colourless or white, and pink rose quartz, purple amethyst, and brown or gray smoky quartz.
  • Quartz is the second most abundant mineral in Earth’s crust.
  • Quartz makes up much of

sand and granites.

feldspar
Feldspar
  • The most abundant family of minerals in Earth’s crust. (over 60%)
  • 3 major properties:
  • Two directions of cleavage
  • 6 on Mohs hardness scale
  • Pearly luster
  • Al ions have replaced some of the Si ions in the basic silica tetrahedron
  • The also have K, Na, and Ca ions.
  • Two major groups of feldspars: potassium feldspars and sodium calcite feldspars.
  • The most common potassium feldspar is orthoclase
  • The sodium-calcite feldspars are called plagioclase
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Mica
  • Soft silicates found in many rocks
  • Flat shiny flakes are easily picked out of rocks such as granite and gneiss
  • Muscovite mica is silvery white
  • Biotite mica is dark brown or black
  • 2.5 on Mohs hardness scale
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Talc
  • The softest mineral
  • 1 on Moh’s hardness scale
  • White, gray, or greenish in colour
  • One good cleavage and a soapy feel
amphiboles
Amphiboles
  • Complex silicate minerals that tend to form long, needlelike crystals
  • Hornblende is the most common, it is shiny dark green, brown, or black. It has two good cleavages at oblique angles, and a hardness of 5 to 6.
  • Hornblende is an example of a ferromagnesian silicate which all contain atoms of iron and magnesium.
pyroxenes
Pyroxenes
  • Right angle cleavage surfaces
  • Augite is the most common member of the pyroxene family. It is a ferromagnesian silicate. Dark green, brown, or black. Two good cleavages, hardness 5 to 6.
  • Poorer luster than hornblende, short stout crystals
olivine
Olivine
  • Olive-green ferromagnesian silicate
  • Glassy shell-like in fracture
  • Very hard (6.5-7.5)
  • Found in some meteorites
garnets
Garnets
  • Dark red, brown, yellow, green, or black
  • Very hard (6.5-7.5)
  • Used as abrasives and gems
kalinite or kaolin
Kalinite or kaolin
  • Aluminum silicate
  • Formed from weathering of feldspar or other silicates
  • Principle mineral in clay and shale
  • Pure kaolin is white, but impurities make it yellow
  • Earthy (crumbly) fracture
  • Hardness between 1 and 2.5
  • Feels greasy and has earthy odour
carbonate minerals calcite and dolomite
Carbonate Minerals:Calcite and Dolomite
  • These minerals are not silica tetrahedrons
  • The carbonate group is CO32-
  • A carbonate mineral is made of carbonate groups joined with various metal ions
  • Limestone and marble are carbonate minerals
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The most common carbonate mineral is calcite, calcium carbonate (CaCO3 )
  • Pure calcite is colourless or white, impurities make it almost any colour
  • Hardness of 3
  • Three perfect oblique cleavages
  • Dolomite is calcium magnesium carbonate
iron oxides and sulfides
Iron Oxides and Sulfides
  • Some minerals have large amounts of iron
  • Iron tends to be combined with either oxygen or sulfur to form an oxide or a sulfide
  • Hematite is the most common iron oxide mineral, it has a hardness of 5-6, is red with an earthy luster and crumbly fracture.
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Magnetite is a black magnetic iron oxide
  • Hardness 5.5-6.5
  • Lodestone is a highly magnetic variety
  • Pyrite is iron sulfide, it is the most common sulfide mineral
  • It has a golden colour and a metallic luster, and is commonly known as fool’s gold