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Matter and Minerals Minerals: Building blocks of rocks • • • • Naturally occurring Solid Inorganic Definite chemical composition • Crystal structure due to internal arrangement of atoms http://www.minerals.net/gemstone/index.htm General Facts about Minerals • Between - 3,000 have been identified • A few are “native elements” made of only one element, such as sulfur, gold copper, and graphite (carbon) • Most are compounds, especially the silicate group (Si, O) • Other important groups are oxides, carbonates, and sulfides Less than a dozen are common in most rocks • Quartz • Feldspar (group) • Muscovite (white mica) • Biotite (black mica) • Calcite • Pyroxene • Olivine • Amphibole (group) • Magnetite, limonite, and other iron oxides • Pyrite How we identify minerals? • Physical properties: Color Luster Hardness Crystal shape Cleavage Specific gravity Other Physical Properties of Minerals • Color: – Most obvious, but often misleading – Different colors may result from impurities Example: Quartz A mineral can be many different colors Below is Mica Many minerals can be the same color Below are gold colored minerals Which one is gold? Physical Properties of Minerals • Color: Streak – color of a mineral in powdered form (used for metallic minerals) Obtained by scratching a mineral on a piece of unglazed porcelain Example: Hematite Gold • When gold is run across a streak plate it makes a yellowish-gold color Quartz is one of the most common mineral in Earth’s crust! Silica (Si) and Oxygen (O) are the only elements within pure quartz Quartz can be found in all sorts of rocks Most sand is made of quartz because it is hard and does not weather away easily Some pieces of quartz are white like milk but most are clear like glass, sometimes with a little pink or grey tinge of color Quartz Shape: Trigonal (Perfect crystals are usually 6-sided prisms with a pyramid shape at the end However, it is much more common to find many crystals that have grown in a mass or broken crystals.) Luster: vitreous Color: Colorless or white Some varieties are pink or smoky Streak: White Hardness: Cleavage: None Fracture: Conchoidal Minerals • • Quartz Silica tetrahedra alone can form a neutral threedimensional framework structure with no need for other cations This arrangement forms a very stable structure popular as ornamental stone and as gemstones •Amethyst is the purple gemstone variety •Citrine is a yellow to orange gemstone variety that is rare in nature but is often created by heating Amethyst •Milky Quartz is the cloudy white variety •Rock crystal is the clear variety that is also used as a gemstone •Rosey Quartz is a pink to reddish pink variety •Smoky quartz is the brown to gray variety Mineral Groups Non-ferromagnesian Silicates (K, Na, Ca, Al) Ferromagnesian Silicates (Fe, Mg) Oxides Carbonates Sulfides/sulfates Native elements Minerals There are a few important groups of non-silicate minerals Only the carbonates are significant as rock-forming minerals The remaining mineral groups are often ore minerals and provide economic sources for various elements The important non-silicate groups are: – – – – – Carbonates Evaporites Oxides Sulphides Phosphates Minerals Non silicates: • • • • Carbonates Co3 The important carbonates are the minerals calcite and dolomite Both are significant rock-forming minerals The calcite group Calcite (Calcium Carbonate) • • • • Magnesite(Magnesium Carbonate) Rhodochrosite (Manganese Carbonate) Siderite(Iron Carbonate) Smithsonite (Zinc Carbonate) Minerals Non silicates: • Evaporites: including the minerals halite, and fluorite; Sulphates including the minerals gypsum and anhydrite The most famous halide mineral, halite (NaCl) or rock salt Minerals Non silicates: • Evaporites •Fluorite: CaF2, Calcium Fluoride Minerals Non silicates: •Gypsum:CaSO4-2(H2O), Hydrated Calcium Sulfate Minerals Non silicates: • • Oxides oxides (hematite and magnetite) Fe2O3, Iron Oxide • • • • hydroxides (limonite and goethite) important minor constituents in rocks aluminum oxide bauxite can also occur as a rock-forming mineral oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium Minerals Non silicates: • • • • Sulphides The mineral pyrite is the only sulphide that occurs commonly in rocks Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc FeS2, Iron Sulfide Minerals Non silicates: • • • • Sulphides The mineral pyrite (FeS2) is the only sulphide that occurs commonly in rocks Sulphides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum and zinc Galena, Chalcopyrite Minerals Non silicates: • • Phosphates are relatively rare The only important phosphate mineral is apatite Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate Common minerals • the most common minerals you'll find in rocks (rock forming minerals) • This pile contains plagioclase feldspar, potassium feldspar, quartz, muscovite mica, biotite mica, amphibole, olivine, and calcite Acknowledged sources 1.www.specialconnections.k u.edu/ /cs/ /caseb_rocks _minerals.ppt – 2.www.earth2class.org/er/students/Mi nerals.ppt 3.www.lwr.kth.se/Grundutbi ldning/AE2401/ /review %20minerals.ppt 4.www.sci.uidaho.edu/geol1 11/Geology %20101/minerals_II_jh [...]... hardest mineral, so it scratches every mineral Physical Properties of Minerals • Crystal shape (or form): – external expression of a mineral s internal atomic structure – planar surfaces are called crystal faces – angles between crystal faces are constant for any particular mineral Quartz Pyrite Physical Properties of Minerals • Cleavage vs Fracture: – The way a mineral breaks – Cleavage: tendency of a mineral. .. silicates MINERAL GROUP Framework Silicate Framework Silicate Sheet Silicate Chain Silicate Chain Silicate Isolated Silicate Isolated Silicate Sulphide Sulphide Sulphide Oxide Oxide Sulphide Oxide Element MINERAL Quartz Feldspar Mica Amphibole Pyroxene Olivine Garnet Sphalerite Chalcopyrite Pyrite Magnetite Hematite Galena Pitchblende Native Gold SPECIFIC GRAVITY 2.6-2.7 2.6-2.7 2.8 -3. 0 2.9 -3. 2 3. 2 -3. 6 3. 3-4.4... Example: mica Physical Properties of Minerals • Cleavage (2 directions): orthoclase amphibole Physical Properties of Minerals • Cleavage (3 directions): halite calcite Physical Properties of Minerals • Cleavage (4 directions): fluorite Physical Properties of Minerals • Fracture: – minerals that do not exhibit cleavage are said to fracture – smooth, curved surfaces when minerals break in a glass-like manner:... 2.6-2.7 2.6-2.7 2.8 -3. 0 2.9 -3. 2 3. 2 -3. 6 3. 3-4.4 3. 5-4.4 4.0 4.2 5.0 5.2 5 .3 7.2 9.5 12.4 Physical Properties of Minerals • Other properties: – reaction with hydrochloric acid (calcite fizzes) – taste (halite tastes salty) – feel (talc feels soapy, graphite feels greasy) – magnetism (magnetite attracts a magnet) Mineral Groups • Rock-forming minerals – ~30 common minerals make up most rocks in Earth’s crust... over 98% of the crust Mineral Groups Element Abundances SILICATES Silica (SiO4)4- Common cations that bond with silica anions All others: 1.5% Common Silicate mineral groups mineral Olivine formula (MgFe)2SiO4 cleavage none Pyroxene (Mg, Fe) SiO3 Amphiboles: Eg hornblende Mica Muscovit e Biotite (Ca2Mg5)Si8O22(OH)2 two cleavage planes at 900 Two planes at 600and 1200 One plane KAl3Si3O10(OH)2 Silicate... surfaces when minerals break in a glass-like manner: conchoidal fracture Quartz Physical Properties of Minerals • Specific gravity: – weight of a mineral divided by weight of an equal volume of water – metallic minerals tend to have higher specific gravity than non-metallic minerals Galena SG=7.5 Quartz SG=2.67 Mineral properties • PHYSICAL CHARACTERISTICS: Specific Gravity S.G is an easily measured physical... of weakness – Minerals that do not exhibit cleavage are said to fracture Do not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken Physical Properties of Minerals • Cleavage is described by: – Number of planes – Angles between adjacent planes – These are constant for a particular mineral Physical Properties of Minerals • Cleavage... One plane KAl3Si3O10(OH)2 Silicate structure Single tetrahedron chains Double chains sheets K(MgFe)3Si3O10(OH) 2 Feldspars:K-feldspar Orthoclase, microcline KAlSi3O8 Two planes at 900 Three dimensional networks none Three dimensional network (Ca,Na)AlSi3O8 Plagioclase Quartz SiO2 Common Non Silicate mineral groups group Oxides member Magnetite Haematite Corundum Sulphides Galena Sphalerite Pyrite Sulfates... blood • The mineral was named hematite because it looked like it was bleeding when it was taken across a streak plate Physical Properties of Minerals • Luster: – How a mineral surface reflects light – Two major types: • Metallic luster • Non-metallic luster Metallic example: Galena Non-metallic example: Orthoclase Pyrite has metallic luster Quartz has vitreous luster Physical Properties of Minerals •... Sulphides Galena Sphalerite Pyrite Sulfates Gypsum Anhydrite Native elements Gold Silver Copper Sulfur Graphite Halides Halite Flourite Carbonates Calcite formula Fe3O4 Fe2O3 Al2O3 PbS ZnS FeS2 CaSO4.H2O CaSO4 Au Ag Cu S C NaCl CaF2 CaCO3 uses Ore of iron Ore of iron Abrasive Ore of lead Ore of zinc Fool’s gold Used for plaster Precious metal Precious metal Used for Wires Used in chemicals pencils Common
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