Coal contains many different microscopic components. Determining some attributes of coal may require microscopic examination, called petrography, which is a subset of petrology. Scientists who examine coal under a microscope are called coal petrographers. In one type of petrography, coal is ground down into fine particles, combined with epoxy, and put into molds to form a pellet. The pellet is then polished and examined under a microscope using reflected, or incident, light. Coal can also be cut into thin sections, as in mineral and rock petrography. A thin section is a thinly cut sample, which is epoxied on to a thin glass plate. The sample side is then ground down and polished to the point at which light is visible through the glass and sample, which allows petrographers to see great details in the samples.
Types of petrography used in coal analysis include:
- Vitrinite reflectance: Used to determine rank of coal and maturation (degree of heating) of hydrocarbon source rocks.
- Maceral composition: Used to determine the relative abundance of microscopic components of coal, called macerals.
- Mineral matter: Used to identify specific minerals and mineral form, and determine the composition and distribution of mineral matter in coal.
- Coal preparation and beneficiation: Like mineral matter, used to determine distribution of mineral matter in association with washability tests to see if and how mineral matter might be removed from the coal.
- Coking properties: Used to examine the distribution of reactive and inert components in coal to determine a coal’s ability to make coke for steel manufacturing.
- Palynology: Used to identify microfossil spores and pollen in the coal for correlation and interpretation of coal origins.
- To learn more about coal composition go to What’s in coal?
If you have specific questions about this analysis, please contact Cortland Eble.