PETROGRAPHIC WEB ATLAS FOR METALLURGICAL BITUMINOUS COAL MACERALS

An online atlas containing approximately 140 labeled photomicrographs of metallurgical bituminous coal macerals has been developed by the U.S. Geological Survey (USGS) in collaboration with the coal petrography subcommittee of the American Society for Testing and Materials (ASTM). The photomicrograph atlas is accessible to the public at the following website: (http://energy.er.usgs.gov/coal_studies/organic_petrology/photo_atlas.html). The site serves primarily as a supporting document for users of ASTM Standard D 2799: Standard Test Method for Microscopical Determination of the Maceral Composition of Coal, and will help lower the degree of subjectivity involved in maceral identification. As requested by the ASTM subcommittee, the atlas will assist workers in the organic petrology discipline with the consistent identification of macerals by portraying their common morphologies, textures, and colors. The website will also serve as a resource for students learning to identify macerals and perform petrographic analyses on coals.

Photomicrographs were taken of 13 coal samples from Colorado and West Virginia in white light using a Leica DFC 480 digital camera attached to a Leica DMRX incident light microscope. The reflectance and maceral composition of each sample were previously determined by 10-15 petrographers through an inter-laboratory round robin exercise conducted by the commercial laboratory CoalTech Petrographic Associates, Inc. Macerals in the photomicrographs were identified and labeled according to definitions in ASTM Standard D 2799, and coal provenance and reflectance values were indicated on each picture. Labeled photographs were reviewed online by the petrography subcommittee for accuracy. Liptinites identified in the atlas include sporinite and cutinite, and inertinite macerals identified include fusinite, semifusinite, inertodetrinite, and micrinite. Photomicrographs of vitrinite range in mean maximum reflectance from 0.70% - 1.79% and were all taken with the same camera exposure to illustrate the color change that occurs with thermal maturation. Planned future work includes the addition of photomicrographs to illustrate coals classified as lignite and anthracite, and the portrayal of other types of organic materials found in hydrocarbon source rocks.