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What is a mineral?

Part 2

Lesson 1

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Focus Questions

  1. How did these crystals grow so large?
  2. What makes diamonds so special?
  3. What properties does diamond have?

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VOCABULARY

  1. Luster
  2. Hardness
  3. Mohs Hardness Scale
  4. Cleavage
  5. Fracture
  6. Streak
  7. Texture
  8. Density
  9. Specific Gravity

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Identifying Minerals

Geologists identify minerals using tests based on a mineral’s physical and chemical properties:

  • crystal form,
  • luster,
  • hardness,
  • cleavage and fracture,
  • streak,
  • color,
  • specific gravity,
  • texture,
  • density, and
  • special properties.

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Identifying Minerals

Crystal Form

  • Distinct crystal shapes = immediate recognized.
  • ID based only on crystal form is rare.

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Identifying Minerals

Luster

  • Luster - way mineral reflects light from surface.
    • two types—metallic & non-metallic
    • Luster not definitive

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Identifying Minerals

Hardness

  • Hardness - measures how easily a mineral is scratched.
  • Mohs scale of Hardness – scale to measure hardness w/ knowns .

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Identifying Minerals

Mohs Scale of Hardness

Mineral

Hardness

Hardness of Common Objects

Diamond

10

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Corundum

9

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Topaz

8

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Quartz

7

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Feldspar

6

Steel file = 6.5

Apatite

5

Glass = 5.5

Fluorite

4

Iron nail = 4.5

Calcite

3

Copper = 3.5

Gypsum

2

Fingernail = 2.5

Talc

1

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Write in Notes

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Identifying Minerals

Cleavage and Fracture

  • Cleavage- splits along one or more planes
    • # of cleaved planes & angle or angles between them makes a difference.
  • Fracture- break w/rough, arclike, or jagged edges

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Identifying Minerals

Streak

  • Streak - color of a mineral powder.
    • streak test, rubbing mineral against unglazed porcelain plate, better for metallic minerals.
    • minerals must be softer than porcelain plate.

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Identifying Minerals

Color

  • Color most noticeable property of a mineral.
  • Least reliable clues of a mineral’s identity.

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Identifying Minerals

Special Properties

Several special properties 4 identification purposes.

  • magnetism,
  • iridescence,

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Identifying Minerals

Special Properties

  • double refraction
  • effervescence with hydrochloric acid, and
  • fluorescence.

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Identifying Minerals

Texture

  • Texture- how a mineral feels to the touch,
    • subjective.
    • combination w/ other tests to identify mineral.

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Identifying Minerals

Density and Specific Gravity

  • Two minerals of the same size may have different weights due to a difference in density.
  • Density – Mass per unit volume
  • d= m/v; d- density, m- mass, v- volume

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Identifying Minerals

Density and Specific Gravity

  • Specific gravity- ratio of the mass of a substance to the mass of an equal volume of water at 4°C.

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