Geology Reference
In-Depth Information
As an example of how this method has been used to further characterize minerals nucleated from coal-fire gas
adjacent to five gas vents, we can look at specimens that were analyzed by XRD (samples from Wuda coalfield in
Inner Mongolia analyzed by Stracher et al. (2005)). At vent numbers 1 and 4 in the Wuda coalfield, the minerals
godovikovite and tschermigite, respectively, were identified. Each vent sample had several other minerals present
and thus consisted of complex mixtures. Godovikovite and tschermigite are nitrogen-bearing phases with the
stoichiometry of NH
4
(Al,Fe
3+
)(SO
4
)
2
and NH
4
Al(SO
4
)
.
12H
2
O, respectively. The total nitrogen content of the
mineral assemblages at vents 1 and 4 were measured to be 0.327
0.03% by weight,
respectively. Using the formula weights of godovikovite (251.5 g/mole) and tschermigite (453.0 g/mole), it was
determined that godovikovite comprised ~6% by weight of the vent 1 mineral assemblage and tschermigite ~14%
by weight of the vent 4 assemblage. Although these numbers are not as spectacular to look at as spectral curves and
the electron micrographs (images) discussed above, they give more precise quantitative meaning to the char-
acterization of mineral assemblages nucleated at coal-fire gas vents.
0.02% and 0.427
+
+
Comments
T
he first question asked when looking at a coal-fire vent sample is
The above methods are often the
first line of defense in solving the problem. Once the mineral assemblage is identified, the question that follows is
“
“
What is it?
”
The same analytical techniques and other methods cam be employed, but
an increase in the level of rigor and time is required. Both questions are simple at face value, but not necessarily
simple to answer if the constraints on characterization are few. The identification and quantification of coal-fire
mineral assemblages is an important step that leads to a better understanding of the role of coal fires in today
How much of each mineral is present?
”
s
environment and in the geologic past. Using the above specialized methods allows the researcher to establish a
more accurate understanding of these complex mineral occurrences.
'
Acknowledgments
A
uthors Paul A. Schroeder and Chris Fleisher thank Glenn B. Stracher, East Georgia College, Swainsboro, for the
opportunity to participate in coal-fires mineral research and for his insightful editing skills. XRD and EMPA
facilities are supported by the Department of Geology, University of Georgia, Athens. Matt Hastings and John
McCormack, Department of Geological Sciences and Engineering, University of Nevada, Reno, contributed to
data collecting. We also acknowledge the National Science Foundation Program for Collaborative Research:
Kamchatka Geothermal Microbial Observatory, MCB-MO-0238407.
Important Terms
Ammonium cation
A positively charged polyatomic structure comprised of a nitrogen
atom with
four
bonded
hydrogen
atoms
in tetrahedral
coordination.
Angstrom
A unit of length used to describe the scale of atoms. It is equal
to one 10-billionth of a meter or one-tenth of a nanometer, i.e.,
10
-
10
m.
Atomic planes
A two-dimensional arrangement of two or more atoms on a flat
surface.
Backscattered electrons
Produced by incident electrons deflected by the positive nuclei of
atoms in a specimen. The electrons scattered back out of the sample
at 180° (nearly parallel to the beam) with no appreciable loss of
energy are then detected. The efficiency of scattering is related to
the mass of the nucleus such that sample areas with heavier ele-
ments appear brighter in a backscattered electron image.
Biomineralization
The process by which living organisms produce minerals. Con-
trolled mineralization is the case where an organism specifically
precipitates a mineral to harden or support tissues (bones or shells).
Induced mineralization is the case where a mineral precipitates in,
