Geology Reference
In-Depth Information
Table 1.1.5
Minerals identified in coal.
Sample
Bituminous
PRB
wt.% mm
*
Units
wt.% mm
No. of Samples
3
1
Quartz
12
27
Kaolinite
13
19
Illite
13
8
Montmorillonite
<
1
2
Feldspar
<
1
2
Silicates
27
29
Pyrite
16
1
<
Sulfides
1
1
<
<
Siderite
1
1
Calcite
3
-
Carbonates
2
<
1
Rutile/anatase
<
1
3
Phosphates
<
1
6
Source: After Senior et al. (2000).
PRB, Powder River Basin.
*
wt.% mm=weight % of mineral matter.
Table 1.1.6
An estimate of the average ultimate composition of coal by rank (wt.%).
Coal rank
C
H
N
O
Peat
56
5.8
1.4
36
Lignite
69
4.6
1.2
25
Bituminous
86
5.4
1.6
7.5
Anthracite
94
2.5
1.0
2.3
Source: After Tatsch (1980) and Mott (1942).
organically bound, in pyrites and in inorganic sulfates. Oxygen, which can be in the organic and inorganic portions
of the coal, is determined by difference. The ultimate composition of coal on a moisture and mineral matter-free
(mmmf) basis is the hypothetical pure coal substance.
Macroscopic and Microscopic
On a macroscopic scale, most large coal deposits are described as banded, exhibiting layers which represent
variations in the plant material or its degree of biochemical alteration. These coals are termed autochthonous and
were formed in situ. Allochthonous or drift coals are those in which plant material was carried into the area of
deposition. Two types of drift coals are cannel coal formed from plant spores and boghead coal formed from the
remains of algae. Drift coals tend to be smaller deposits and have a higher concentration of mineral matter
(
>
10%). (Hessley et al., 1986)
Stopes (1919) described banded coals by what he called lithotypes. Vitrain was a bright glassy band, formed from
wood or bark. Clarain was a smooth interlaminated band of bright and dull coal; no specific origin was postulated.
Durain was a dull black band and was very hard. In contrast, fusain was a charcoal-like band, porous, friable, and
frequently containing mineral matter.
