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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 2 - 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 do 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.
Pyrite or “Fool’s Gold” When pyrite is run across a streak plate, it has a black or dark green streak. Pyrite is not worth much money, while gold is worth a lot. They look alike, so miners call it fool’s gold.
Hematite Hematite’s color is grey, but its streak is red. Hema means 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 Hardness: –How easy it is to scratch a mineral –Mohs Scale of Hardness relative scale consists of 10 minerals, ranked 1 (softest) to 10 (hardest)
Gypsum is soft, it can be scratched by a fingernail.
Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a coin
Fluorite is harder. It can be scratched by a nail, but not a coin or fingernail.
Diamond is the 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 to break along planes 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 (1 direction): 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: 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 property that can be readily estimated. In general, sulphides and oxides have much higher specific gravities than silicates. MINERAL GROUPMINERALSPECIFIC GRAVITY Framework SilicateQuartz2.6-2.7 Framework SilicateFeldspar2.6-2.7 Sheet SilicateMica2.8-3.0 Chain SilicateAmphibole2.9-3.2 Chain SilicatePyroxene3.2-3.6 Isolated SilicateOlivine3.3-4.4 Isolated SilicateGarnet3.5-4.4 SulphideSphalerite4.0 SulphideChalcopyrite4.2 SulphidePyrite5.0 OxideMagnetite5.2 OxideHematite5.3 SulphideGalena7.2 OxidePitchblende9.5 ElementNative Gold12.4
–reaction with hydrochloric acid (calcite fizzes) Physical Properties of Minerals Other properties: –taste (halite tastes salty) –feel (talc feels soapy, graphite feels greasy) –magnetism (magnetite attracts a magnet)
Rock-forming minerals –~30 common minerals make up most rocks in Earth’s crust –Composed mainly of the 8 elements that make up over 98% of the crust Mineral Groups
All others: 1.5% Element Abundances Silica (SiO 4 ) 4- SILICATES Common cations that bond with silica anions
mineralformulacleavageSilicate structure Olivine(MgFe) 2 SiO 4 none Single tetrahedron Pyroxene(Mg, Fe) SiO 3 two cleavage planes at 90 0 chains Amphiboles: Eg. hornblende (Ca 2 Mg 5 )Si 8 O 22 (OH) 2 Two planes at 60 0 and 120 0 Double chains Mica Muscovit e KAl 3 Si 3 O 10 (OH) 2 One planesheets Biotite K(MgFe) 3 Si 3 O 10 (OH) 2 Feldspars:K-feldspar Orthoclase, microcline KAlSi 3 O 8 Two planes at 90 0 Three dimensional networks Plagioclase (Ca,Na)AlSi 3 O 8 QuartzSiO 2 noneThree dimensional network Common Silicate mineral groups
groupmemberformulauses Oxides Sulphides Sulfates Native elements Halides Carbonates Magnetite Haematite Corundum Galena Sphalerite Pyrite Gypsum Anhydrite Gold Silver Copper Sulfur Graphite Halite Flourite Calcite Fe 3 O 4 Fe 2 O 3 Al 2 O 3 PbS ZnS FeS 2 CaSO4.H2O CaSO4 Au Ag Cu S C NaCl CaF 2 CaCO3 Ore of iron Abrasive Ore of lead Ore of zinc Fool’s gold Used for plaster Precious metal Used for Wires Used in chemicals pencils Common salt Used in chemicals Used in cement Common Non Silicate mineral groups
–Oxides O 2- –Carbonates(CO 3 ) 2- –Sulfides S 2- –Sulfates(SO 4 ) 2- –HalidesCl -, F -, Br - –Native elements(single elements; e.g., Au) Mineral Groups Silicates (most abundant) Non-silicates (~8% of Earth’s crust):
Mineral Groups – Silicates Silicates –Tetrahedron fundamental building block 4 oxygen ions surrounding a much smaller silicon ion Silicon-oxygen tetrahedron (SiO 4 ) 4-
Mineral Groups – Silicates Joining Silicate Structures –How tetrahedra may be linked: independent tetrahedra single chains double chains sheets 3-D framework
Mineral Groups – Silicates –
Olivine Group dark silicates (Fe-Mg) Mineral Groups – Silicates No cleavage ferromagnesian
The Olivine group is composed of three minerals, with the following formulas: Forsterite = Mg 2 SiO 4 Olivine (Chrysolite) = (Mg,Fe) 2 SiO 4 Fayalite = Fe 2 SiO 4 The intermediate variety, Olivine, is not scientifically recognized as a separate mineral, but is nevertheless mentioned. Magnesium iron silicate. The series ranges from the magnesium end member, Forsterite, through the intermediate member, Olivine (also known as Chrysolite), to the iron end member, Fayalite Composition
Color Olive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, white StreakColorless Hardness6½ - 7 Crystal Forms and Aggregates Usually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses. grains grainy TransparencyTransparent to translucent Specific Gravity3.2 - 4.2 LusterVitreous Cleavagenone FractureConchoidal TenacityBrittle
Uses The variety Peridote is a famous gem. It creates a distinctive, yellow-green to olive-green gem that is well known. It is the birthstone for August. Olivine is also used as a flux for making steel, and is an ore of magnesium. Striking FeaturesColor, localities, and hardness Complex TestsSoluble in hydrochloric acid
Pyroxene Group Ferromagnesian / dark silicates (Fe-Mg) Mineral Groups – Silicates 2-directions of cleavage (at nearly 90 degrees) Augite
Minerals The typical pyroxene structure contains chains of SiO 3 tetrahedrons The slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90 o degrees (actually 93 o and 87 o ).
Pyroxene minerals are common in in meteorites and the extrusive igneous rock called basalt. There are many different types of pyroxene including augite, wollastonite, diopside, enstatite, and hypersthene. All of the types contain Si 2 O 6 but some have sodium (Na) while others have iron (Fe), magnesium (Mg), or a combination of these three elements. The general properties of the more common pyroxene minerals, such as augite, are listed below. Shape:Orthrorhombic or Monoclinic Luster: Glassy or metallic Color: Black Streak: White, light green or light brown Hardness: 5-6.5 on Mohs hardness scale Cleavage: Two planes that meet at nearly a 90-degree angle Fracture: Most have uneven and brittle fractures.
Amphibole Group Ferromagnesian / dark silicates (Ca, Fe-Mg) Mineral Groups – Silicates 2-directions of cleavage (not at 90 degrees) Hornblende
There are several different minerals within the amphibole group, but the most common type is hornblende. You can find small crystals of hornblende in many types of igneous rocks. They often look like little dark specks. Hornblende (Ca 2 Mg 5 )Si 3 O 22 (OH) 2 Shape: Monoclinic (crystals look like short, six-sided columns) Luster: Glassy or milky Color: Black or dark green, translucent to opaque Streak: Grey-green or grey-brown Hardness: 5-6 Cleavage: Two planes that meet at a 124-degree angle Fracture: Uneven brittle fracture
Mica Group and Clay Minerals light silicates (K, Al) Mineral Groups – Silicates 1-direction of cleavage Muscovite non-ferromagnesian
Minerals Micas and Clay Minerals Sheets of tetrahedra are the building blocks. Aluminum is also involved in thesesheet structures which are charge- balanced by the cations Mg, Na and K. most common mica minerals:muscovite, biotite
Mica minerals make some rocks sparkle! They are often found in igneous rocks such as granite and metamorphic rocks such as schist. They sparkle because light is reflected on their flat surfaces, which are where the mineral breaks along its plane of cleavage. These minerals break so easily along their cleavage that some crystals have broken into many thin layers that look like the pages of a little book.
Biotite K(MgFe) 3 Si 3 O 10 (OH) 2 Shape: Monoclinic. Forms flat plates. Luster: Pearly, metallic Color: Dark brown, dark green or black Streak: White Hardness: 2.5-3 Cleavage: Yes, one plane of cleavage Fracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks. Muscovite KAl 3 Si 3 O 10 (OH) 2 Shape: Monoclinic. Forms flat plates. Luster: Pearly, metallic Color: Colorless or lightly tinted Streak: White Hardness: 2-3 on Mohs Hardness Scale Cleavage: Yes, one plane of cleavage Fracture: This mineral is also flexible and doesn’t fracture very easily.
Feldspar Group light silicates (K-Na-Ca, Al) Mineral Groups – Silicates 2-directions of cleavage (at 90 degrees) Orthoclase Plagioclase K-feldspar Ca/Na-feldspar Most common mineral group
Minerals Feldspar group A second group of alumino- silicates, tetrahedra form three-dimensional frameworks with Ca, Na and K as the balancing cations. The very abundant feldspar are K-Na bearing alkali The K-feldspars or alkali felspars: Microcline, (Potassium aluminum silicate) Orthoclase, (Potassium aluminum silicate)
Feldspar is the most common mineral in the Earth’s crust, so you are very likely to find it in the rocks you collect! It is found it all of the three rock types, but is most common in intrusive igneous rocks like granite where the crystals look white or pink. There are several types of feldspar. The characteristics of the two most common types are listed below. These two common types of feldspar are difficult to tell apart besides their color. Color can be helpful, but beware because the same mineral can often have different colors. The sure way to tell these two apart is by looking at the crystal surfaces for thin parallel groves called striations. Plagioclase feldspar has striations but orthoclase feldspar does not.
Orthoclase K AlSi 3 O 8 Shape: Monoclinic (Flat tabular or prism-shaped crystals) Luster: Glassy or pearly Color: Cream to pink Streak: White Hardness: 6 on Mohs Hardness Scale Cleavage: perfect Fracture: brittle Plagioclase CaNaAlSi 3 O 8 Shape: Triclinic (Single prism-shaped crystals are very rare. You are much more likely to find many crystals that have grown together in a mass. Luster: Glassy or pearly Color: White to gray Streak: White Hardness: 6-6.5 Cleavage: perfect Fracture: brittle
Quartz light silicates (pure SiO 2 ) Mineral Groups – Silicates no cleavage (conchoidal fracture) hard, resistant to weathering Quartz
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: 7 Cleavage: None Fracture: Conchoidal
Minerals Quartz Silica tetrahedra alone can form a neutral three- dimensional 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 Ferromagnesian Silicates (Fe, Mg) Non-ferromagnesian Silicates (K, Na, Ca, Al) 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
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.plagioclase feldsparpotassium feldspar quartzmuscovite micabiotite micaamphiboleolivine calcite