Transcript Crystal Interfacial Angles

Crystal Interfacial Angles
• Even when the crystals are different sizes, angles
between equivalent faces are the same
• For different minerals, angles are different.
3
2
4
4
3
1
2
Quartz
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1
Habit
Habit - distinctive shape of the way the mineral
commonly (habitually) appears
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Concentric shells -- malachite
Habit
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Crystal shape and Habit result from
internal atomic structure
N. Lindsley-Griffin, 1998
Cleavage - tendency to break along
planes of weak bonds
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Mica cleaves along planes
of the weakest bonds
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Fracture describes how a mineral
breaks on an irregular surface rather
than along cleavage planes
Types of fracture:
Smooth
Rough
Splintery
Conchoidal
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Hardness
Hardness -- the resistance to being scratched
Mohs scale measures relative hardness,
the ability of one mineral to scratch another
Diamond
Corundum
Topaz
Quartz
Feldspar
Apatite
Fluorite
Calcite
Gypsum
Talc
10
9
8
7
6
5
4
3
2
1
Steel file
Glass
(6.5)
(5.5- 6)
Copper penny
Fingernail
(3.0)
(2.5)
Mohs hardness scale: 1 = softest mineral; 10 = hardest
© Houghton Mifflin 1998; Lindsley 2000
The 10 minerals of
Mohs relative hardness scale
3 Calcite
1 Talc
4 Fluorite
2 Gypsum
9 Corundum
6 Feldspar
N. Lindsley-Griffin, 1999
5 Apatite
7 Quartz
8 Topaz
10
Diamond
Luster
Luster - the appearance of a mineral
in reflected light
Types of luster:
Metallic
Nonmetallic
Pearly
Vitreous
Resinous
Silky
Dull
Earthy
Metallic luster of
pyrite
© Houghton Mifflin; N. Lindsley-Griffin, 1998.
Earthy luster of
limonite
Metallic Luster is characteristic of ore minerals
and others that contain metal cations.
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Resinous luster
in sphalerite
Pearly luster
in talc
N. Lindsley-Griffin, 1999