Geology Reference
In-Depth Information
3.1. Spontaneous Combustion
and Coal Petrology
Maria Mastalerz
Agnieszka Drobniak
James C. Hower
Jennifer M.K. O'Keefe
Assemblage of Cretaceous resinite in a
high volatile A Liposzii coal, Russia.
Photo by James C. Hower, 2008.
Introduction
M
acerals, the microscopically identifiable organic constituents of coal, are one of three basic parameters that
define coal. The other two parameters are the coal rank, the measure of metamorphism of the organic constituents,
and the inorganic content of the coal, most visibly seen as the minerals associated with coal. Below we briefly
present the basic concepts of coal petrology and discuss coal parameters that have been noted as potential triggers
for spontaneous combustion.
Maceral Composition of Coal
M
acerals are microscopically recognizable organic entities in coal and sedimentary rocks. They were introduced by
analogy to minerals in rocks. There is, however, a major difference between the concept of minerals and macerals.
In contrast to minerals that have homogeneous composition and unchangeable internal structure, macerals consist of
a mixture of organic compounds that, in addition, undergo both physical and chemical changes during coalification.
Macerals in coal are distinguished microscopically by color, shape, morphology, and degree of preservation of cell
structure, reflectance level, and the intensity of fluorescence. These differences between macerals result from
different parent material (e.g., different plant parts), different depositional environment, or preservation.
Macerals are classified into three groups: vitrinite/huminite, inertinite, and liptinite (Table 3.1.1). These maceral
groups are each subdivided into maceral subgroups and macerals. Several standardized systems of nomenclature
exist worldwide. These classification systems are variations of the system established by the International
Committee for Coal and Organic Petrology (ICCP, 1998, 2001; Sykorova et al., 2005), the organization that
develops and revises coal petrology terminology and nomenclature.
The vitrinite group (Figure 3.1.1) represents woody plant material (e.g., stems, trunks, roots, and branches),
derived from lignin and cellulose of plant tissues. Telovitrinite represents intact compressed fragments of woody
material of varying degree of compaction. The remains of the cell structure must be visible to distinguish this
maceral subgroup. Detrovitrinite results from smaller fragments, shows higher degree of degradation, and usually
forms groundmass for other macerals. Gelified material produced before or during coalification becomes gelovi-
trinite, a relatively rare maceral in the coal.
The liptinite group (Figure 3.1.2) includes components that are chemically more resistant to physical and
chemical degradation than other macerals such as pollen, spores, cuticles, waxes, and resins. Liptinite
