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.