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Rock Forming Minerals Minerals are important because every inorganic item that has been manufactured originated from a mineral. Minerals are inorganic, naturally occurring substances that have a characteristic chemical composition, distinctive physical properties, and crystalline structure. Crystalline structure is an orderly three-dimensional arrangement of atoms or molecules, and materials with crystalline structure form crystals. A few “minerals” do not have crystalline structure and so don’t form crystals – these are called mineraloids. Most mineral crystals occur in rocks, which are simply defined as an aggregate of one or more minerals. In this lab, we will investigate some rock-forming minerals. In this lab, the minerals are organized based on their chemical composition. The most common are listed below. Classification Scheme for Minerals (Groups) □ Elements – minerals composed of a single element, such as Gold (Au), Silver (Au) – usually metals or metalloids □ Sulfides & related compounds – minerals that contain sulfur as S or S2 □ Haloides – minerals that contain halides such as chlorine (Cl), fluorine (F): halite is the mineral that is mined to make table salt, and is represented by NaCl □ Oxides – minerals that contain oxygen (O, as in Rutile TiO; O2, O3, O4) & Hydroxides – minerals that contain (OH) □ Carbonates – minerals containing CO3 □ Sulfates – minerals that contain sulfur as SO4 □ Phosphates – minerals that contain phosphorus (P) as PO4 □ Silicates – minerals that contain silica in the form of SiO2,SiO4, Si2O6, Si3O8, Si3O10, or any combination of Silicon (Si) and Oxygen (O) □ Organic – often not “true” minerals, as minerals must be inorganic. This category includes Amber (fossil tree sap), fossils, shell material, pearls, coral, bone, etc. Characteristics of Minerals Color is a mineral’s most easily observed property – but is not really all that useful for identifying minerals. Many minerals are produced in a range of colors, based on the impurities that are included in their atomic makeup. Minerals also vary in clarity; they may be transparent (clear, like window glass), translucent (“foggy”), or opaque (not possible to see through). Crystal form describes the three-dimensional geometric shape that a mineral assumes. Often, we can infer the crystal form if only a portion of the shape is visible or the crystal is broken. Perfect crystals only grow when they are totally unrestricted during growth. Most of our lab specimens will not be perfect crystals, but we can still determine their identity by performing other tests. Minerals are said to be cryptocrystalline when the crystals the specimen is composed of are too small to be seen without magnification. Hardness is a measure of resistance to scratching. A harder surface will scratch a softer one. A quantitative scale of hardness was developed by Frank Mohs where the softest mineral (talc) has a hardness of 1 and the hardest mineral (diamond) has a hardness of 10. Higher numbered minerals will scratch lower numbered ones. Hard minerals can scratch glass and soft minerals cannot. Mohs Scale of Hardness Hardness of some common objects: HARD 10 – Diamond 9 – Corundum (sapphire, ruby) 8 – Topaz 7 – Quartz 6 – Orthoclase or Feldspar 5 – Apatite SOFT 4 – Fluorite 6.5 Streak Plate 5.5 Glass, masonry nail, knife blade 4.5 Wire (iron) nail 3 – Calcite 3.5 Copper wire or coin (penny) 2 – Gypsum 2.5 Fingernail 1 – Talc Streak is the color of a substance after it has been ground or scratched to make a fine powder. The easiest way to do this is by scratching the mineral across a plate of unglazed porcelain. Some minerals are hard enough that it can be difficult to get a good streak. If you can’t get a good streak, test the hardness – if it is greater than 7, the white streak you see is likely from the streak plate and not the mineral. Luster is a description of how light reflects from the surface of an object (such as a mineral). Luster can be described as “metallic” or “non-metallic”. The luster of “nonmetallic” minerals can be described in further detail as: “vitreous” – resembling the luster of freshly broken glass; “waxy” – resembling the luster of a candle; “pearly” – resembling the luster of a pearl; “satiny” – resembling the luster of satin or silk cloth; “earthy” – lacking reflection, completely dull, like dry soil; “greasy” resembling the luster of grease, oily; or “porcelaneous” – resembling the luster of porcelain. Cleavage is the tendency for some minerals to break (cleave) along flat, parallel surfaces (cleavage planes). The cleavage planes are parallel surfaces of weak chemical bonding (attraction) between repeating, parallel layers of atoms in a crystal, and more than one set of cleavage planes can be present in a crystal (as many as 6). Fracture refers to any break in a mineral that does not occur along a cleavage plane – fractures are not normally flat and never occur in parallel sets. Magnetism can influence some minerals. Test for magnetism by putting a magnet near the mineral. If it attracts, it is magnetic, and you may be able to attract small metal objects with it (such as paperclips). This is a special property of some minerals. Reaction with hydrochloric acid is different among minerals. All carbonate minerals (those with carbonate, CO3) will effervesce (fizz) when acid is dropped onto them. Some minerals (such as Dolomite) will only react once powdered (such as with a steel nail). We will not perform an acid test in this lab. * missing information is intentional. white white 7 non-metallic non-metallic non-metallic Garnet Gypsum Halite 7 non-metallic Olivine 1 non-metallic, greasy. Talc white whtie greybrown Some Uses Plaster of Paris, wallboard, drywall, art sculpture medium (alabaster). Used as an abrasive, on sandpaper, as a gemstone (birthstone for January). Used to make ceramics, glass, enamel, soap, false teeth, scouring powders. Gemstone (peridot) for August. Ore of magnesium metal. Used for fire-resistant tiles, rubber, paint. Ore of iron for steel, brass, bronze, tools, vehicles, nails and bolts, bridges, etc. Red pigment. Ore of iron for steel tools, vehicles, nails and bolts, bridges, etc. Color white, gray, pale green or brown. No cleavage. Feels greasy or soapy. Very soft. Used for talcum powder, facial makeup, ceramics, paint, sculptures. Usually colorless, white or gray but uncommon varieties occur Used as an abrasive, used to make glass, in all colors. Transparent to translucent. No cleavage gemstones (Purple - Amythyst - Februrary, (concoidal fracture) Forms hexagonal pyramids and prisms. Orange -Citrine) Color brass yellow ("fools gold"). Opaque. Tarnishes brown. Ore of sulfur, for sulfuric acid, explosives, Forms cubes or eight-sided polygons. No cleavage. fertilizers, pulp processing, insecticides. Color silvery-gray, black or brick red. Tarnishes red. Opaque. Soft (earthy) and hard (metallic) varieties have same streak. Forms thin crystals or is massive. color silvery gray to black. Opaque. Forms 8 sided polyhedrons. Tarnishes gray. No cleavage. Magnetic? Color black, green-black or brown-black. Cleavage excellent. Can split into thin, flexible sheets. Color pale or dark olive-green to yellow, or brown. Forms short crystals that may resemble sand grains. Concoidal fracture. Cleavage absent. Colorless, white, yellow, brown, blue or red. Transparent to Table salt, road salt; used in water softeners translucent. Forms cubes, but may be massive. Cleavage is and as a preservative. Sodium Ore. ___________________________. Salty taste (don't lick!) Color orange, brown, white, green or pink. Cleavage excellent in two directions at nearly 90degrees. Color usually red, black, or brown; sometimes yellow, green, pink. Forms 12 sided polyhedron. No cleavage. Translucent to opaque. Colorless, white or gray. Forms blade shapes or needles. Transparent to translucent. Very soft. Cleavage good. Usually colorless, white or yellow, but may be green, brown, or Used to make antacid tablets, fertilizer, pink. Opaque or transparent. Excellent cleavage in 3 cement; ore of calcium. directions not at 90 degrees. Reaction to HCl? Distinctive Properties * some spaces have been left blank where you are required to determine these properties during lab. 7 non-metallic, greasy. Quartz 6 - 6.5 2.5 - 3 non-metallic Mica (biotite) Pyrite 6 Metallic Magnetite (Fe3O4) 1.5 - 6 metallic or nonmetallic Hematite (Fe2O3) 2 white 6 non-metallic Feldspar white white Streak non-metallic Hardness Calcite Luster Properties of 12 Rock-Forming Minerals Answer Sheet for Lab 2 Name: _______________________ Rock-Forming Minerals Date: _______________________ Instructions: Please fill in your answers for the lab on this lab sheet. No red pens or markers. --------------------------------------------------------------------------------------------------------------------The minerals in this lab are labeled by name. Your teacher will instruct you to investigate each of the minerals. The objective of today’s lab is to learn some of the most common minerals, and how to identify them. Define Mineral: (hint – there are 5 characteristics to a mineral) ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ ______________________________________________________________________________ Define Rock: ______________________________________________________________________________ Mineral ID Lab: Galena PbS Pyrite FeS2 Sulfur S Do a streak test for each of these minerals. What are their streak colors? Galena _________________ Pyrite _________________ Sulfur _________________ What kind of luster do they have? ________________________________________________ Do these minerals have cleavage or fracture? Write next to mineral name above. What is the hardness of these minerals? Galena _________________ Pyrite _________________ Sulfur _________________ Fluorite CaF2 Halite NaCl Copper Cu (native element) Do a streak test for each of these minerals. What are their streak colors? Fluorite _________________ Halite _________________ Copper _________________ Do these minerals have cleavage or fracture? Write next to mineral name above. What kind of luster do they have? ________________________________________________ What is the hardness of these minerals? Fluorite _________________ Halite _________________ Copper _________________ Hematite Fe3O4 Magnetite Fe2O3 Quartz SiO2 Which of these minerals is magnetic? _________________ What kind of luster do they have? ________________________________________________ Do these minerals have cleavage or fracture? Write next to mineral name above. Do a streak test for each of these minerals. What are their streak colors? Hematite _________________ Magnetite _________________ Quartz _________________ What is the hardness of these minerals? Hematite _________________ Magnetite _________________ Quartz _________________ Calcite CaCO3 Olivine (Mg,Fe)2[SiO4] Kaolin Al2Si2O5(OH)4 Do a streak test for each of these minerals. What are their streak colors? Calcite _________________ Olivine _________________ Kaolin _________________ What kind of luster do they have? ________________________________________________ Do these minerals have cleavage or fracture? Write next to mineral name above. What is the hardness of these minerals? Calcite _________________ Olivine _________________ Kaolin _________________ Gypsum CaSO4·2H2O Talc Mg3[(OH)2|Si4O10] Graphite C (considered a native element made of Carbon) Do a streak test for each of these minerals. What are their streak colors? Gypsum _________________ Talc _________________ Graphite _________________ What kind of luster do they have? ________________________________________________ What is the hardness of these minerals? Gypsum _________________ Talc _________________ Graphite _________________ Do these minerals have cleavage or fracture? Write next to mineral name above. Silicates – Bonus Impress Me Questions! Augite (Ca,Mg,Fe)[(Si,Al)2O6] Horneblende Ca2Na(Mg,Fe2)4(Al,Fe3)[(Si,Al)4O11][OH]2 Biotite Muscovite K(Mg,Fe)3[(OH,F)2|AlSi3O10] KAl2[(OH,F)2|AlSi3O10] Potassium Feldspar K[AlSi3O8] Plagioclase Feldspar nNa[AlSi3O8] + nCa[Al2Si2O8] Garnet Kyanite Olivine Talc Quartz Fe3Al2[SiO4]3 Al2[O|SiO4] (Mg,Fe)2[SiO4] Mg3[(OH)2|Si4O10] SiO2 The silicates are a very diverse and complex group of minerals. What do they ALL have in common? _____________________________________________________________________ Can you distinguish differences between the minerals in the mica group by visually observing them? What about their chemistry causes this difference? (I told you about the visual differences!) ______________________________________________________________________________ Summary – Impress Me Some More! Which group would ICE (yes, the crystal form of water) be a part of? _________________ Organic materials that are often considered minerals (but are not) are coal and amber. Why aren’t they minerals? (hint: what criteria of “mineralness” do they not meet?) ______________________________________________________________________________ ______________________________________________________________________________ Is a shell a mineral? Shells are often made of aragonite (like snails and clams) or calcite (sea urchins). Why or why not? ________________________________________________ Look at the following samples, and fill in the chart for them below. Using the charts in the introduction and your notes taken during lab, identify the minerals. # Luster Hardness Cleavage Color/Streak Special Identification 1 2 3 * For luster, choose metallic, glassy, earthy, or greasy. * For streak, report color that is found when the mineral sample is rubbed on a porcelain plate.