Chapter 2
MINERALS|
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Chapter 2 MINERALS |
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Beryl and pyrite on quartz |
Minerals are the fundamental building blocks of the Earth and make up rocks, which have recorded the history of the Earth. Minerals and rocks are essential for human existence; all of our resources are derived from rocks/minerals or from living things that depend on rocks/minerals/soil. In addition, minerals are used for investment and jewelry.
| KEY TO MINERAL SETS | ||||
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Chemical Group |
Mineral Name |
Specimen Number |
Chemical Composition |
Silicate Type |
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Chloride |
(11) |
NaCl |
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Sulfides |
(3) |
ZnS |
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(4) |
PbS |
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(5) |
FeS2 |
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Oxides |
(1) |
Fe2O3 |
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(2) |
Fe2O3·nH2O |
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Carbonates |
(9) |
CaCO3 |
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Sulfate |
(8) |
CaSO4·2H2O |
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Silicates |
(18) |
Fe, Mg, Si, O |
single |
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(17) |
Ca, Fe, Mg, Si, O |
chain |
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(16) |
Ca, Fe, Mg, Al, Si, O, H2O |
chain |
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(14) |
K, Al, Si, O, H2O |
sheet |
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(15) |
K, Fe, Mg, Al, Si, O, H2O |
sheet |
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(10) |
Al, Si, O, H2O |
sheet |
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(7) |
SiO2 |
3-D |
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(12, 13) |
K, Na, Ca, Al, Si, O |
3-D |
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1. HEMATITE - earthy variety called "red ocher"
Composition: Fe2O3
Diagnostic features:
Streak: reddish-brown
Luster: earthy
(Other properties vary widely.)
Occurrence: formed under a wide variety of conditions and associated with the main kinds of rocks.
Use: most important ore of iron, red pigment, polishing powder.
Name: from a Greek word meaning blood.
HEMATITE - specular variety, with metallic luster.
Composition: Fe2O3
Diagnostic features:
Streak: reddish-brown
Luster: metallic
(Other properties vary widely.)
Occurrence: formed under a wide variety of conditions and associated with the three kinds of rocks.
2. LIMONITE - yellow ocher
Composition: Fe2O3·nH2O
Diagnostic features:
Streak: yellow-brown
(Other properties vary widely.)
Occurrence: formed by alteration of previously existing iron minerals.
Use: pigment, minor source of iron
Name: from a Greek word meaning meadow, in allusion to its occurrence in bogs.
3. SPHALERITE
Composition: ZnS
Diagnostic features:
Color: yellow to brown and black
Hardness: 3.4 to 4
Chemical test: powder is decomposed in hydrochloric acid with evolution of hydrogen sulfide gas.
Streak: light yellow to white
Occurrence: in igneous rocks and in veins in limestone; associated with galena, pyrite, and fluorite.
Use: the most important ore of zinc.
Name: from the Greek word meaning treacherous or uncertain, because it resembles galena but yields no lead.
4. GALENA
Composition: PbS (almost always contains silver.)
Diagnostic features:
Color: lead gray
Hardness: 2.5
Specific gravity: 7.5 (heavy)
Luster: metallic
Cleavage: cubic
Occurrence: in igneous rocks and in veins in limestone, associated with sphalerite and fluorite.
Use: practically the only source of lead and an important ore of silver.
Name: from the Latin word meaning lead ore.
5. PYRITE
Composition: FeS2
Diagnostic features:
Color: brass yellow (fool's gold)
Hardness: 6 to 6.5 (hardness of gold is 2.5 to 3)
Streak: greenish-black or brownish-black.
Crystal form: cubic crystals are sometimes observed, bearing parallel striations.
Occurrence: found in all three kinds of rocks.
Use: in manufacture of sulfuric acid.
Name: from the Greek word meaning fire, in allusion to the fact that when struck with steel it gives off brilliant sparks.
Composition: CuFeS2
Diagnostic features:
Color: brass yellow, but often tarnished to bronze or iridescent.
Hardness: 3.5 to 4 (less than pyrite).
Streak: greenish-black
Crystal form: usually massive, crystals not observed.
Occurrence: usually found in veins in igneous rocks.
Use: the most widely occurring copper mineral and one of the most important sources of copper.
Name: derived from the Greek word meaning copper and from pyrite.
7. QUARTZ
Composition: SiO2
Diagnostic features:
Hardness: 7
Luster: glassy
Conchoidal fracture (no cleavage)
(May or may not occur as crystals.)
Occurrence: next to feldspar, the most abundant mineral of the Earth's crust; found in all three kinds of rocks.
Use: radio and radar "crystals", ornamental, manufacture of glass and many other uses.
Name: the name quartz is a German word of ancient derivation.
QUARTZ - rose variety
This is another variety of quartz.
Some others: amethyst, citrine, cat's eye, rock crystal (hexagonal crystals).
QUARTZ - variety called chert.
This is still another variety of quartz; but in this variety, the crystals are too fine to be seen. It is similar to flint, but is light in color rather than dark. It is found mainly in sedimentary rocks.
8. GYPSUM - variety "rock gypsum" occurs in granular masses.
Composition: CaSO4·2H2O
Diagnostic features:
Color: light colored or transparent
Hardness: 2 (can be scratched with fingernail)
Occurrence: commonly found in sedimentary rocks; formed under evaporitic conditions.
Use: Plaster of Paris, gypsum lath, fertilizer, ornamental (variety called alabaster).
Name: from the Greek word (name) for the mineral.
GYPSUM - variety "selenite gypsum" is found in crystalline form.
Compared with muscovite (#14), selenite gypsum is softer and cleaves into tabular plates which can be bent but are not elastic as are muscovite and biotite.
9. CALCITE
Composition: CaCO3
Diagnostic features:
Color: usually colorless to white, but other colors occur.
Hardness: 3
Cleavage: good along three inclined planes.
Chemical test: effervesces freely in cold, dilute hydrochloric acid.
Occurrence: chief constituent of limestone, chalk, and marble.
Use: chiefly in manufacture of cement, also decorative, and in optical instruments.
Name: from the Latin word calx meaning burnt lime.
10. KAOLINITE
Composition: hydrous aluminum silicate.
Diagnostic features:
Color: white
Feel: greasy
Smell: earthy
Found in small masses.
Note: does not react to acid, as does the rock chalk.
Occurrence: results from the alteration of other aluminum silicates, particularly feldspar.
Use: paper, china, brick.
Name: kaolinite is derived from kaolin, which is a corruption of the Chinese word kauling meaning high ridge, the name of a hill near Jauchu Fa where the mineral is obtained.
11. HALITE
Composition: NaCl
Diagnostic features:
Hardness: 2.5
Cleavage: cubic
Taste: salty
Feel: "damp"
Soluble in water
Occurrence: precipitated from sea water under evaporitic conditions and found in sedimentary rocks.
Use: common table salt; source of sodium.
Name: from the Greek word meaning salt.
Composition: KAlSi3O8
Diagnostic features:
Hardness: 6
Color: usually pink or white
Luster: vitreous
Cleavage: two good at 90°
Occurrence: orthoclase and the other feldspars are the most abundant minerals in the Earth's crust; found in all three kinds of rocks but most commonly in igneous rocks.
Use: in manufacture of porcelain.
Name: orthoclase refers to the right angle cleavage; feldspar is derived from the German word feld meaning field.
13. PLAGIOCLASE FELDSPAR - The term "plagioclase feldspar" refers to a continuous gradational series of minerals which range in chemical composition from pure sodic plagioclase, called albite, to pure calcic plagioclase, called anorthite.
Composition: NaAlSi3O8 to CaAl2Si2O8
Diagnostic features:
Color: white to gray
Hardness: 6
Luster: vitreous
Cleavage: two good at approximately 94°.
Occurrence: found in igneous, metamorphic, and more rarely in sedimentary rocks.
Use: in ceramics, semi-precious stones.
Name: from the Greek word meaning oblique in allusion to the oblique angle between the cleavage planes.
14. MUSCOVITE MICA
Composition: complex hydrous potassium aluminum silicate.
Diagnostic features:
Color: colorless to white or silvery
Cleavage: one perfect
Large flakes are elastic
Occurrence: characteristic of igneous rocks and also found in metamorphic and sedimentary rocks.
Use: electrical insulation, heat insulation.
Name: Muscovite was so called from the popular name of the mineral muscovy glass, because of its use as a glass substitute in Muscovy. Mica was probably derived from the latin micare meaning to shine.
Composition: complex hydrous potassium iron magnesium aluminum silicate.
Diagnostic features:
Color: dark green brown, black
Cleavage: one perfect
Large flakes are elastic
Occurrence: same as muscovite
Name: in honor of the French physicist, J. B. Biot.
16. HORNBLENDE - One of a number of similar minerals collectively referred to as the amphibole group.
Composition: complex hydrous calcium magnesium iron aluminum silicate.
Diagnostic features:
Color: dark green to black
Hardness: 5 to 6
Cleavage: two at angles of 56° and 124°
Crystals: frequently prismatic
Occurrence: in igneous rocks and metamorphic rocks.
Name: from an old German word for any dark prismatic mineral occurring in ores but containing no metal.
17. AUGITE - One of a number of similar minerals collectively referred to as the pyroxene group.
Composition: complex calcium magnesium iron silicate.
Diagnostic features:
Hardness: 5 to 6
Cleavage: two at angles of 87° and 93°.
Crystals: short, prismatic
Occurrence: in igneous and metamorphic rocks.
Name: from the Greek word meaning luster.
18. OLIVINE
Composition: (Mg, Fe)2SiO4
Diagnostic features:
Color: olive green to black
Hardness: (of individual, separate grains) 6.5 to 7.
Luster: vitreous
Occurrence: found mainly in igneous rocks.
Use: as the semi-precious gem peridot.
Name: from olive green color.
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