Systematic Classification of Silicate Minerals
Dr. James Martin-Hayden, EEES-1010
Silicate
Silica
Content
Structure
(%SiO2)
Isolated
Silicates
Single
Chain
Silicates
Double
Chain
Silicates
Sheet
Silicates
Example Mineral
Olivine
Amphibole◊ Group
(e.g., Hornblende)
Mica Group
(e.g., Biotite◊)
(e.g., Muscovite◊)
content
‡
25-50% 18-26%
0-16%
50-60%
‡
15-22%
0-9%
39%
39%
‡
18-33%
0%
6%
20%
0%
21%
0%
0%
10-19%
10% †
0%
(†)
†
†
†
Clay Group
(e.g., Kaolinite)
Framework
Silicates
Fe/Mg‡
Content
‡
~50%
~16%
Pyroxene# Group
(e.g., Augite)
46%
†
Feldspar Group,
◊
‡Ferromagnesians
Al†
#
Plagioclase(Na -Ca )
Orthoclase (K◊)
Quartz (pure SiO2◊)
43-69%
76%
100%
0%
0%
Cleavage
Density
†Alluminosilicates
Hardness
Color
Occurrence
none
Comprises
~4 g/cm3
most of the
green Mantle
6½
2 (90o)
~3.3
Found in basalt
Oceanic Curst
5½
black with Ca-Plag.#
o
o
2 (120 -60 )
~3.3
Found in
Continental
5½
black Crust◊
~3.0
Found in
1 (perfect)
black Continental
◊
2½ 2.8 slvr Crust
Microscopic
2.6
From chemical
platelets
green weathering of
or gray silicates*
2 (90o)
2.6
Ca Plag.# in
wht-blk Oceanic Crust
6 2.7 pink Others
Contin◊.
Concentrated
none (fracture) 2.6
white in Continental
7
to gray Environments
Isolated Silicates
Single Chain Silicates
Double Chain Silicates
Sheet Silicates
General trends toward bottom: Increasing SiO2, Decreasing Fe/Mg, Lighter in density, Lighter in Color
Other Trends
#Oceanic crust (basalt) is mostly pyroxene and Ca-plagioclase (Ca-Feldspar) and thus more dense and dark.
◊Continental crust (e.g., granite) contains minerals rich in silica, low in iron, and thus less dense and light in color.
Melting points (and crystallization temperature) decrease toward bottom.
Framework Silicates
(e.g., quartz melts first and is the last to crystallize, ~700oC. Pyroxene and Ca-plagioclase ~1000oC)
Rate of chemical weathering decreases toward bottom of the chart or
Resistance to chemical weathering increases toward bottom.
Chemical
(e.g., quartz is extremely resistant to chemical weathering)
Weathering
*All silicates (except quartz) are converted to clay minerals by chemical weathering.
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