Geoscience Reference
In-Depth Information
Table 9.6
Typical main mineral hardness values of various rock types (after Waltham, 1994).
Hardness
Mineral
Specific gravity
Origin
Sedimentary
Metamorphic
Igneous
√
√
√
7
Quartz
2.7
√
√
6
Feldspar
2.6
√
6
Hematite
5.1
√
6
Pyrite
5.0
√
6
Epidote
3.3
√
5.5
Mafics
3.0
>
√
√
5.0
Limonite
3.6
√
3.5
Dolomite
2.8
√
√
3.0
Calcite
2.7
√
√
√
2.5
Muscovite
2.8
√
√
2.5
Biotite
2.9
√
√
2.5
Kaolinite
2.6
√
2.5
Illite
2.6
√
2.5
Smectite
2.6
√
2.0
Chlorite
2.7
√
2.0
Gypsum
2.3
Table 9.7
Mudstone - shale classification (Spears, 1980).
Quartz content
Fissile
No fissile
>
40%
Flaggy (parting planes 10-50 mm apart) Siltstone
Massive siltstone
30-40%
Very coarse shale
Very coarse mudstone
20-30%
Coarse shale
Coarse mudstone
10-20%
Fine shale
Fine mudstone
10%
Very fine shale
Very fine mudstone
<
9.8 Relative change in rock property due to discontinuity
•
The discontinuities in a rock have a significant effect on its engineering properties.
•
=
Rock mass strength
intact strength factored for discontinuities. Similarly for
other properties.
Table 9.8
Relative change in rock property.
Rock property
Change in intact property due to discontinuity
Typical range
Typical magnitude change
Strength
1-10
5
Deformation
2-20
10
Permeability
10-1000
100
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