Environmental Engineering Reference
In-Depth Information
TABLE 5.2
Common Rock-Forming Minerals and Their Chemical Composition
Group
Mineral
Variety
Chemical Composition
Comments
Silicates
Feldspars
Orthoclase
KAlSi
3
O
8
Very abundant
}
Variable
Plagioclase
NaAl
2
Si
3
O
8
CaAl
2
Si
2
O
8
Micas
Muscovite (white mica)
KAl
2
(Si
3
Al)O
10
(OH)
2
Very abundant
Biotite (dark mica)
K
2
(MgFe)
6
(SiAl)
8
O
20
(OH)
4
Ferromagnesian mineral
a
Amphiboles
Hornblende
Na, Ca, Mg, Fe, Al silicate
Ferromagnesian mineral
a
Pyroxenes
Augite
Ca, Mg, Fe, Al silicate
Ferromagnesian mineral
a
Olivine
(MgFe)
2
SiO
4
Ferromagnesian mineral
a
Hydrous silicates
Kaolinite
Al
2
Si
2
O
5
(OH)
4
Secondary origin
b
Oxides
Quartz
SiO
2
Very abundant
Aluminum
Al
2
O
3
Iron oxides
Hematite
Fe
2
O
3
a
Limonite
2Fe
2
O
3
3H
2
O
Magnetite
Fe
3
O
4
c
Carbonates
Calcite
CaCO
3
Very abundant
Dolomite
CaMg(CO
3
)
2
Sulfates
Gypsum
CaSO
4
2(H
2
O)
Anhydrite
CaSO
4
a
Ferromagnesian minerals and the iron oxides stain rock and soils orange and red colors upon chemical
decomposition.
b
Hydrous silicates form from previously existing minerals by chemical weathering and include the clay min-
erals (such as kaolinite and the chlorites). serpentine, talc, and zeolites.
c
Magnetite occurs in many igneous rocks and provides them with magnetic properties even though often dis-
tributed as very small grains.
TABLE 5.3
Textural Classification of Mineral Grains
Class
Size Range (mm)
Recognition
Very coarse-grained
2.0
Grains measurable
Coarse-grained
0.6-2.0
Clearly visible to eye
Medium-grained
0.2-0.6
Clearly visible with hand lens
Fine-grained
0.06-0.2
Just visible with hand lens
Very fine-grained
0.06
Not distinguishable with hand lens
Anisotropic: the fabric has planar or linear elements from mineral cleavage, foli-
ations, or schistose, and the properties vary with the fabric orientation.
●
Mineral Identification Factors
Crystal Form
Distinct crystal form is encountered only occasionally in rock masses. Some common min-
erals with distinct forms are garnet, quartz, calcite, and magnetite.
Color
Clear or light-colored minerals include quartz, calcite, and feldspar. Dark green, dark
brown, or black minerals contain iron as the predominant component.
