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Guided Notes on Identifying Minerals
Chapter 4, Section 2
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To identify minerals, geologists rely on several relatively simple tests, which are based on a mineral’s physical and chemical properties.
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Color
What causes it? the presence of trace elements
How reliable is it? It is one of the least reliable clues to a mineral’s identity.
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Luster
Definition:the way that a mineral reflects light from its surface
Two types: metallic and nonmetallic
What causes it? Differences in the chemical composition of minerals cause different lusters
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Texture
Definition: how a mineral feels to the touch
Examples: fluorite has a smooth texture, talc has a greasy texture
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Streak
Definition: the color of a mineral when powdered
How useful is it? It is one of the most reliable clues to a mineral’s identity
What are its limitations? It only works on minerals that are softer than porcelain
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Hardness
Definition: how easily a mineral can be scratched
What causes it? Hardness is caused by the arrangement of a mineral’s atoms
How reliable is it? Hardness is one of the most reliable clues to a mineral’s identity
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Cleavage
Definition: when a mineral splits evenly along one or more flat planes
What causes it? Weak atomic bonds in one or more direction
Examples: mica has perfect cleavage, halite has cubic cleavage
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Fracture
Definition: breaking unevenly with rough edges
What causes it? Tightly bonded atoms
Examples: quartz has irregular fracture, flint has conchoidal fracture
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Density
Definition: mass per unit of volume
What causes it? Differences in atomic weight and structure
How is it expressed? A ratio of mass divided by volume (g/mL)
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Double Refraction
Definition: the refraction of a single ray of light into 2 images
What causes it? The arrangement of atoms in a mineral
Which minerals exhibit it? Calcite (Iceland Spar) and zircon
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Magnetism
Which mineral exhibits it? magnetite
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Describe how the Mohs scale of hardness is used…
Any mineral with a greater hardness than other mineral will scratch the softer mineral
The Mohs scale places common minerals in order of hardness, ranging from 1 to 10
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Describe how scientists use specific gravity…
Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water.
Specific gravity is used as a measure of density because it contains easily understood numbers for comparison
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A mineral is called an ore if it contains a useful substance that can be mined at a profit.
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Ores located deep inside the earth are removed by underground mining. Ores near the surface are obtained from open-pit mines. If the cost of removing waste material from a mine becomes higher than the value of the mineral, then the mineral is no longer considered an ore.
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Gems are valuable minerals prized for their rarity and beauty. The beautiful colors of gemstones are caused by the presence of trace elements.