Geology Reference
In-Depth Information
where the liquid reaction product X(l) solidifies to X(s);
React
Reacts with
substrate
∑
SGC
!
X
ð
l
Þ !
Y
ð
s
Þþ
Altered substrate
ð
9
:
1
:
9
Þ
where X(l) reacts with the substrate to form the solid Y(s); and
React
React with substrate
or each other
∑
SGC
!
-
X
ð
s
Þ
-
Y
ð
l
Þ
-
Z
ð
g
Þ !
W
ð
s
Þ
-
Altered substrate
ð
9
:
1
:
10
Þ
where the solid, liquid, and gas reaction products X(s), Y(l), and Z(g) react with the substrate or each other to form
the solid W(s).
Discussion
T
he above reactions exemplify mineral-forming processes at gas vents, they are not all inclusive, and additional
processes are possible. As a simple example, consider reaction (9.1.2) rewritten as
Y
1
(s)
Condenses
X(g)
⎯⎯⎯⎯⎯⎯→
X(l)
Y
2
(s)
In this case, subsequent to condensation, two solid phases Y
1
(s) and Y
2
(s), perhaps in a drip or flow condensate,
nucleated simultaneously from a liquid phase at its eutectic temperature.
The absence of a mineral assemblage at or in the vicinity of a coal-fire gas vent does not imply that it
never formed. Many assemblages consist of water-soluble powdery materials that are easily dissolved
by rainwater or eroded by wind. Consequently, if the mineralized by-products of combustion are
eroded, it may be extremely difficult to determine whether an altered substrate formed by GSA, GLAS, or
GRLS.
Determining the reactions in the SGC of a coal fire during and after exhalation is a formidable task, yet to be
performed. As burning proceeds, gas composition fluctuates in accordance with chemical diversity in the burning
coal, as well as in the sediment, rock, and aqueous solutions encountered by the gas
to the surface.
Exchange reactions between the gas, sediment, rocks, and solutions continuously change gas chemistry, thereby
influencing, along with temperature and SGC partial pressures,
en route
the mineral assemblages that crystallize in
association with the gas.
The identification of trace elements in minerals formed as a consequence of coal combustion may reveal
certain minerals that are vectors for the transmission of toxins to humans by inhaled dust particles or even by
food grown in soils that contain these minerals. The proliferation and catastrophic effects of coal fires
subsequent to the industrial revolution in Europe include trace elements that promote air, soil, and water
pollution (Stracher and Taylor, 2004). These pollutants have destroyed natural habitats; have killed people;
have forced communities to relocate; and are accountable for human diseases including hyperkeratosis
(arsenic poisoning), dental and skeletal fluorosis (osteosclerosis), thallium poisoning, lung cancer, and
pulmonary heart disease (Johnson et al., 1997, p. 19; World Resources Institute, 1999, pp. 63
-
67; Finkelman
et al., 1999, 2001, 2002; Finkelman, 2004).
