Geology Reference
In-Depth Information
10.1. Sample Identification
and Imaging
Paul A. Schroeder
Chris Fleisher
Glenn B. Stracher
Vesicular mineral assemblage nucleated
from anthracite gas on thermally altered
mudstone at the Centralia mine fire in
Pennsylvania. The assemblage consists
of alunogen, copiapite, voltaite, quartz,
and sulfur.
Photo by Glenn B. Stracher, 2004.
Introduction
T
he gas vents and ground fissures associated with burning waste piles of coal and underground coal beds occur in
isolated areas and form on relatively short-lived geologic time scales. As previously noted (Chapter 9; Stracher
et al., 2005), the types of minerals that form in and adjacent to these gas vents and fissures are related to the
complexities of the (1) burning coal
'
s composition, (2) depth and temperature of burning, (3) chemistry of the
adjacent and overburden rocks and any fluids they contain, and (4) atmospheric conditions when the vented gas is
exhaled at the surface (Figure 10.1.1A). These factors result in rapidly formed crystals (sometimes within a few
days) of unusual chemistry that make the identification of coal-fire minerals a challenging undertaking. Similar
mineral-forming environments that occur in equally complex and isolated locations include terrestrial volcanic
vents, industrial plants that burn coal, and perhaps volcanic vents and fissures on other planets. Methodologies used
to characterize the mineral assemblages at such sites (both remotely and by ground truth) can be employed to study
minerals nucleated from coal-fire gas exhaled from vents and fissures.
Coal-fire gas vents are similar to terrestrial volcanic vents because when exhaled at the surface, hot-reduced gases
come into contact with the cooler oxidizing atmosphere (Figure 10.1.1B). Volcanic vent mineralization sometimes
has a component of biological mediation (Figure 10.1.1B; Kyle et al., 2007), so it is possible that coal-fire mineral
assemblages also contain some aspects of biological mediation. Coal-fire biomineralization is an area that requires
future work. Smokestacks associated with industrial coal burning represent a man-made environment where
similar, yet distinctive, vent-like mineral assemblages occur (Figure 10.1.1). The common process in all of these
environments is the very rapid time scale of mineral formation (particularly in terms of geologic time).
A
Centralia, Pennsylvania, USA
C
Near Emery, Utah, USA
B
Uzon Caldera, Kamchatka, Russia
Figure 10.1.1. Three different environments where similar mineral assemblages are found: (A) Gas vent from the
underground Centralia mine fire, Pennsylvania. Minerals nucleated from the gas, on the ground around the vent, at
the base of the smoke plume. (B) Vent at a volcanic hot spring in Uzon Caldera, Kamchatka, Russia. Thermophilic
bacteria and archaea biologically induce mineralization in the springs (Konhauser and Ferris, 1996). (C) Coal-
burning power plant in Emery County, Utah. Smokestacks are sites where fly ash accumulates and rapid sulfate
mineralization occurs. Photos by Paul A. Schroeder (A) 2006, (B) 2006, and (C) 2005
.
