Geology Reference
In-Depth Information
◗
Figure 3.16
Several Types of Mineral Cleavage
TABLE 3.2
Mohs Hardness Scale
Hardness of Some
Cleavage
in one direction
Cleavage plane
Micas—biotite
and muscovite
a
Hardness
Mineral
Common Objects
10
Diamond
9
Corundum
Cleavage in
two directions
at right angles
Potassium
feldspars,
plagioclase
feldspars
8
Topaz
b
7
Quartz
Steel fi le (6½)
6
Orthoclase
Glass (5½-6)
Cleavage in
three directions
at right angles
Halite,
galena
c
5
Apatite
4
Fluorite
3
Calcite
Copper penny (3)
Fingernail (2½)
Cleavage in
three directions,
not at right angles
Calcite,
dolomite
d
2
Gypsum
1
Talc
Cleavage in
four directions
Fluorite,
diamond
e
◗
Figure 3.18
Graphite and Magnetite
Cleavage in
six directions
f
Sphalerite
◗
Figure 3.17
Cleavage in Augite and Hornblende
Graphite is the mineral used to make pencil “lead” write on
paper.
a
93
87
°
Cross section
Augite crystal and cross section
of crystal showing cleavage.
a
56
°
124
°
Cross section
Magnetite is magnetic. Magnetite is an ore of iron and is used in
toys like Etch A Sketch®.
Hornblende crystal and cross section
of crystal showing cleavage.
b
b
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