Download Ch. 4 Lect. Minerals

Earth Science
Unit 2 Chap. 4 Lecture Notes
B. Rife
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Unit 2 Chapter 4 Minerals
HOMEWORK:
HW 1
Extra Credit HW 2
Topic Questions: PG. 52, 57
Review, Interpret & Apply, Crit. Thinking pg 60-61
Unit 1 Identifying Minerals
Topic 1 Rock-Forming Minerals
Matter consists of protons, neutrons, and electrons.
Matter made up of one kind of atom is an element.
Elements may be combined to form chemical compounds.
Single elements (gold) and chemical compounds (quartz) occur as minerals.
Most frequently as compounds.
Minerals and mixtures of minerals occur as rocks.
Common minerals that make up most of the rocks in Earth’s crust are called rockforming minerals.
The study of minerals and their properties is called mineralogy.
A mineral is a naturally occurring, inorganic, crystalline solid, with a definite
chemical composition.
A mineral is inorganic. (consist of matter that is not plant or animal)
A mineral is natural. (can’t be man made)
A mineral is solid. (solids that have a geometric crystal system - cubic,
hexagonal)
A mineral has an exact chemical composition. (If the chemical composition
changes, the mineral changes)
Minerals are either elements or compounds, and thus can be identified using
chemical symbols and formulas. The formula for quartz, a compound, is
SiO2
Topic 2 Identification by Inspection
Minerals are identified by their physical properties.
Color is a mineral’s most conspicuous characteristic and is largely dependent on
chemical composition and the arrangement of atoms.
Some minerals possess colors that are constant, such as green in malachite, blue
in azurite and metallic yellow in pyrite and gold.
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Unit 2 Chap. 4 Lecture Notes
B. Rife
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Color can be altered by small amounts of impurities. Rubies and sapphires are
variations in composition due to impurities.
Luster refers to the way light is reflected from a mineral’s surface.
Metallic luster - If a mineral looks like a metal, regardless of color. (pyrite, galena)
Nonmetallic luster - is described as dull, pearly (pearl), silky, glassy or vitreous
(quartz), and brilliant or adamantine (diamond).
A crystal is a solid bounded by plane surfaces that has a definite shape due to
its internal atomic arrangement.
Crystal System
Isometric or Cubic
Hexagonal
Tetragonal
Orthorhombic
Monoclinic
Triclinic
Examples
Halite, Galena
Quartz, Calcite
Zircon
Sulfur, Topaz
Hornblend, Orthoclase (white feldspar),
Muscovite (mica)
Albite, Plagioclase (pink feldspar), Turquoise
Topic 3 Identification by Simple Tests
Streak is the color of the powdered mineral. As a rule, the streak of a metallic
mineral is at least as dark as the hand specimen. The streak of a
nonmetallic mineral is usually colorless or white. Minerals of a hardness
of greater than five do not streak. (gold streak is yellow, pyrite is dark)
Cleavage of a mineral is its tendency to split or break along smooth flat planes.
(Muscovite mica)
Fracture is breakage along an irregular surface. The surface may be rough
(quartz) or conchoidal (obsidian)
Hardness - is a mineral’s resistance to being scratched. a mineral’s hardness
depends largely on the strength of bonds between the atoms.
Friedrich Mohs, a German mineralogist, worked out a relative scale of hardness
of ten common minerals used for mineral identification.
Earth Science
Unit 2 Chap. 4 Lecture Notes
B. Rife
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Moh’s Scale of Hardness
Field Scale of Hardness
1
2
3
4
5
6
7
8
9
10
1
soft, greasy, flakes on fingers
2
scratched by fingernail
3
scratched by penny (copper)
4
scratched easily by knife (soft steel)
5
scratched by knife with difficulty
6
scratched by glass
7
scratched by steel file (nail)
8
scratches quartz
No approximations above 8
Talc
Gypsum
Calcite
Fluorite
Apatite
Orthoclase (white feldspar)
Quartz
Topaz
Corundum
Diamond
Topic 4 Specific Gravity
Specific gravity is the ratio of the weight of a mineral to the weight of an equal
volume of water.
Specific gravity is the ratio of the density of the mineral to the density of water.
It is a dimensionless quantity, that is it has no units.
Specific gravity is useful in recognizing heavy minerals and some gem stones.
Gold has a specific gravity (SG) of 19.3 while the SG of pyrite is 5.0
Topic 5 The Acid Test
Calcite is the principal mineral in limestone (sedimentary) and marble
(metamorphic) rocks. Calcite is CaCO3. It reacts with hydrochloric acid
(HCl) by forming CO2 bubbles.
Topic 6 Special Properties of Minerals
Halite (rock salt) tastes salty
Lodestone is a magnet. Magnetite can be picked up by a magnet.
Fluorite and calcite fluorescence (glows) under ultraviolet (“black”) lights.
Carnotite and uraninite (uranium ores) are radioactive.
Sulfur has a specific odor.
Calcite creates double refraction.
Unit II Descriptions of Rock-Forming Minerals
Topic 7 Silicates: From Silica Tetrahedrons
Earth Science
Unit 2 Chap. 4 Lecture Notes
B. Rife
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Silicates are mineral compounds of silicon oxygen combined with other metals
and nonmetals. They make up the largest group of minerals.
a. Quartz is only silicon and oxygen (SiO2). Quartz is the second most
abundant mineral in Earth’s crust.
b. Feldspar are the most abundant family of minerals
Othoclase is a potassium aluminum silicate and usually has a whitish
appearance.
Plagioclase is a sodium calcium silicate and usually has a pinkish
appearance.
c. Micas are soft silicates with a hardness of about 2.5
Muscovite is known as white mica and has a silvery appearance.
Biotite is known as black mica
The above three are principal components of granites (intrusive igneous rocks).
d. Talc is the softest mineral (hardness of 1)
Amphibloes, pyroxenes, olivine, garnets, and kaolin are other silicates.
Topic 8 Carbonates Minerals: Calcite and Colomite
Carbonates are the next largest group of minerals. They contain carbonate (CO3)
and some other element.
Calcite CaCO3 found in limestone and marble.
Dolomite is calcium magnesium carbonate.
Malachite is a copper carbonate with a distinctive green color.
Azurite is a copper carbonate with a distinctive blue color.
Topic 9 Iron Oxides and Sulfides
Oxides are combinations of oxygen and some other element.\
Hematite Fe2O3 is iron ore. Often has a red appearance.
Magnetite is a black magnetic iron oxide.
Pyrite is an iron sulfide with a gold metallic luster, thus called “fool’s gold”
Pyrite can react with water and form sulfuric acid responsible for
“acid mine drainage”