2Minerals: Building blocks of rocks Naturally occurringSolidInorganicDefinite chemical compositionCrystal structure due to internal arrangement of atoms
3General Facts about Minerals Between 2 - 3,000 have been identifiedA 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.
4Less than a dozen are common in most rocks QuartzFeldspar (group)Muscovite (white mica)Biotite (black mica)CalcitePyroxeneOlivineAmphibole (group)Magnetite, limonite, and other iron oxidesPyrite
5How do we identify minerals? Physical properties:ColorLusterHardnessCrystal shapeCleavageSpecific gravityOther
6Physical Properties of Minerals Color:Most obvious, but often misleadingDifferent colors may result from impuritiesExample:Quartz
7A mineral can be many different colors. Below is Mica.
8Many minerals can be the same color. Below are gold colored minerals Many minerals can be the same color. Below are gold colored minerals. Which one is gold?
9Physical 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
10GoldWhen gold is run across a streak plate it makes a yellowish-gold color.
11Pyrite 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.
12Hematite 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.
13Physical Properties of Minerals Luster:How a mineral surface reflects lightTwo major types:Metallic lusterNon-metallic lusterMetallicexample:GalenaNon-metallicexample:Orthoclase
16Physical Properties of Minerals Hardness:How easy it is to scratch a mineralMohs Scale of Hardnessrelative scaleconsists of 10 minerals, ranked 1 (softest) to 10 (hardest)
17Mohs Scale of Hardness Hardest (10) – Diamond Softest (1) – Talc Common objects:- Fingernail (2.5)- Copper coin (3.5)- Wire nail (4.5)- Glass (5.5)- Streak plate (6.5)
18Gypsum is soft, it can be scratched by a fingernail.
19Calcite is soft, but a little harder because it cannot be scratched by a fingernail, but it can be scratched by a coin
20Fluorite is harder. It can be scratched by a nail, but not a coin or fingernail.
21Diamond is the hardest mineral, so it scratches every mineral.
22Physical Properties of Minerals Crystal shape (or form):external expression of a mineral’s internal atomic structureplanar surfaces are called crystal facesangles between crystal faces are constant for any particular mineralQuartzPyrite
23Physical Properties of Minerals Cleavage vs. Fracture:The way a mineral breaksCleavage: tendency of a mineral to break along planes of weaknessMinerals that do not exhibit cleavage are said to fractureDo not confuse cleavage planes with crystal faces! Crystal faces are just on the surface and may not repeat when the mineral is broken.
24Physical Properties of Minerals Cleavage is described by:Number of planesAngles between adjacent planesThese are constant for a particular mineral
25Physical Properties of Minerals Cleavage (1 direction):Example: mica
26Physical Properties of Minerals Cleavage (2 directions):orthoclaseamphibole
27Physical Properties of Minerals Cleavage (3 directions):halitecalcite
28Physical Properties of Minerals Cleavage (4 directions):fluorite
29Physical Properties of Minerals Fracture:minerals that do not exhibit cleavage are said to fracturesmooth, curved surfaces when minerals break in a glass-like manner: conchoidal fractureQuartz
30Physical Properties of Minerals Specific gravity:weight of a mineral divided by weight of an equal volume of watermetallic minerals tend to have higher specific gravity than non-metallic mineralsGalenaSG=7.5QuartzSG=2.67
31Mineral 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 GRAVITYFramework SilicateQuartzFeldsparSheet SilicateMicaChain SilicateAmphibolePyroxeneIsolated SilicateOlivineGarnetSulphideSphalerite4.0Chalcopyrite4.2Pyrite5.0OxideMagnetite5.2Hematite5.3Galena7.2Pitchblende9.5ElementNative Gold12.4
32Physical 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)
33Mineral Groups Rock-forming minerals ~30 common minerals make up most rocks in Earth’s crustComposed mainly of the 8 elements that make up over 98% of the crust
34SILICATES Mineral Groups Common cations that bond with silica anions Element AbundancesSilica(SiO4)4-SILICATESCommon cations thatbond with silica anionsAll others: %
35Common Silicate mineral groups formulacleavageSilicate structureOlivine(MgFe)2SiO4noneSingle tetrahedronPyroxene(Mg, Fe) SiO3two cleavage planes at 900chainsAmphiboles:Eg. hornblende(Ca2Mg5)Si8O22(OH)2Two planes at 600and 1200Double chainsMicaMuscoviteKAl3Si3O10(OH)2One planesheetsBiotiteK(MgFe)3Si3O10(OH)2Feldspars:K-feldsparOrthoclase, microclineKAlSi3O8Two planes at 900Three dimensional networksPlagioclase(Ca,Na)AlSi3O8QuartzSiO2Three dimensional network
36Common Non Silicate mineral groups memberformulausesOxidesSulphidesSulfatesNative elementsHalidesCarbonatesMagnetiteHaematiteCorundumGalenaSphaleritePyriteGypsumAnhydriteGoldSilverCopperSulfurGraphiteHaliteFlouriteCalciteFe3O4Fe2O3Al2O3PbSZnSFeS2CaSO4.H2OCaSO4AuAgCuSCNaClCaF2CaCO3Ore of ironAbrasiveOre of leadOre of zincFool’s goldUsed for plasterPrecious metalUsed for WiresUsed in chemicalspencilsCommon saltUsed in cement
37Mineral Groups Silicates (most abundant) Non-silicates (~8% of Earth’s crust):Oxides O2-Carbonates (CO3)2-Sulfides S2-Sulfates (SO4)2-Halides Cl-, F-, Br-Native elements (single elements; e.g., Au)
38Mineral Groups – Silicates Tetrahedronfundamental building block4 oxygen ions surrounding a much smaller silicon ionSilicon-oxygentetrahedron(SiO4)4-
39Mineral Groups – Silicates Joining Silicate StructuresHow tetrahedra may be linked:independent tetrahedrasingle chainsdouble chainssheets3-D framework
41Mineral Groups – Silicates Olivine Groupdark silicates (Fe-Mg) ferromagnesianNo cleavage
42CompositionMagnesium 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, FayaliteThe Olivine group is composed of three minerals, with the following formulas: Forsterite = Mg2SiO4 Olivine (Chrysolite) = (Mg,Fe)2SiO4 Fayalite = Fe2SiO4 The intermediate variety, Olivine, is not scientifically recognized as a separate mineral, but is nevertheless mentioned.
43ColorOlive-green, yellow-green, light green, yellow, yellow-brown, brown, gray, whiteStreakColorlessHardness6½ - 7Crystal Forms and AggregatesUsually occurs as rounded grains, in dense aggregates of grainy crystals, and as fractured masses.TransparencyTransparent to translucentSpecific GravityLusterVitreousCleavagenoneFractureConchoidalTenacityBrittle
44UsesThe 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 hardnessComplex TestsSoluble in hydrochloric acid
45Mineral Groups – Silicates Pyroxene GroupFerromagnesian / dark silicates (Fe-Mg)Augite2-directionsof cleavage(at nearly 90 degrees)
46MineralsThe typical pyroxene structure contains chains of SiO3 tetrahedronsThe slope of the tetrahedral pyramids helps to determine the cleavage angle of the pyroxenes at nearly 90o degrees (actually 93o and 87o).
47Pyroxene 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 Si2O6 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 MonoclinicLuster: Glassy or metallicColor: BlackStreak: White, light green or light brownHardness: on Mohs hardness scaleCleavage: Two planes that meet at nearly a 90-degree angleFracture: Most have uneven and brittle fractures.
48Mineral Groups – Silicates Amphibole GroupFerromagnesian / dark silicates (Ca, Fe-Mg)Hornblende2-directionsof cleavage(not at 90 degrees)
49There 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 (Ca2Mg5)Si3O22(OH)2Shape: Monoclinic (crystals look like short, six-sided columns)Luster: Glassy or milkyColor: Black or dark green, translucent to opaqueStreak: Grey-green or grey-brownHardness: 5-6Cleavage: Two planes that meet at a 124-degree angleFracture: Uneven brittle fracture
50Mineral Groups – Silicates Mica Group and Clay Mineralslight silicates (K, Al) non-ferromagnesianMuscovite1-directionof cleavage
51Minerals 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
52Mica minerals make some rocks sparkle 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.
53BiotiteK(MgFe)3Si3O10(OH)2Shape: Monoclinic. Forms flat plates.Luster: Pearly, metallicColor: Dark brown, dark green or blackStreak: WhiteHardness: 2.5-3Cleavage: Yes,one plane of cleavageFracture: The mineral is rather flexible and so it doesn’t fracture very easily. In fact you can bend it very far before it breaks.MuscoviteKAl3Si3O10 (OH)2Color: Colorless or lightly tintedHardness: 2-3 on Mohs Hardness ScaleCleavage: Yes, one plane of cleavageFracture: This mineral is also flexible and doesn’t fracture very easily.
54Mineral Groups – Silicates Feldspar Grouplight silicates (K-Na-Ca, Al)K-feldsparMost common mineral groupOrthoclasePlagioclase2-directionsof cleavage(at 90 degrees)Ca/Na-feldspar
55Minerals Feldspar group A second group of alumino-silicates, tetrahedra form three-dimensional frameworks with Ca, Na and K as the balancing cations.The very abundantfeldspar are K-Na bearing alkaliThe K-feldspars or alkali felspars:Microcline, (Potassium aluminum silicate)Orthoclase, (Potassium aluminum silicate)
56Feldspar 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.
57Orthoclase K AlSi3O8Shape: Monoclinic (Flat tabular or prism-shaped crystals)Luster: Glassy or pearlyColor: Cream to pinkStreak: WhiteHardness: 6 on Mohs Hardness ScaleCleavage: perfectFracture: brittlePlagioclase CaNaAlSi3O8Shape: Triclinic (Single prism-shaped crystals are very rare. You are much more likely to find many crystals that have grown together in a mass.Color: White to grayHardness: 6-6.5Cleavage: perfectFracture: brittle
58Mineral Groups – Silicates Quartzlight silicates (pure SiO2)no cleavage(conchoidal fracture)hard, resistant to weatheringQuartz
59Quartz 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.QuartzShape: 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: vitreousColor: Colorless or white. Some varieties are pink or smoky.Streak: WhiteHardness: 7Cleavage: NoneFracture: Conchoidal
60MineralsQuartzSilica tetrahedra alone can form a neutral three-dimensional framework structure with no need for other cations.This arrangement forms a very stable structurepopular as ornamental stone and as gemstonesAmethyst 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.
62Mineral Groups Non-ferromagnesian Silicates (K, Na, Ca, Al) Silicates (Fe, Mg)OxidesCarbonatesSulfides/sulfatesNative elements
63Minerals 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:CarbonatesEvaporitesOxidesSulphidesPhosphates
64Minerals Non silicates: Carbonates Co3 The important carbonates are the minerals calcite and dolomite. Both are significant rock-forming minerals.The calcite groupCalcite (Calcium Carbonate)Magnesite(Magnesium Carbonate)Rhodochrosite (Manganese Carbonate)Siderite(Iron Carbonate)Smithsonite (Zinc Carbonate)
65Minerals The most famous halide mineral, halite (NaCl) or rock salt 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
68Minerals Non silicates: Oxides oxides (hematite and magnetite) Fe2O3, Iron Oxidehydroxides (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.
69Minerals 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
70Minerals 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
71Minerals Non silicates: Phosphates are relatively rare. The only important phosphate mineral is apatite.Ca2Fe(PO4)2 - 4H2O, Hydrated Calcium Iron Phosphate
72Common mineralsthe 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.