The U.S.G.S. Photomicrograph Atlas

Coal and Related Carbon Resources / Lignite, Graphite, Graphene, & Carbon Uses

The Photomicrograph Atlas provides:

• Education – A basic tutorial in the nomenclature of organic materials as they occur in sedimentary rocks such as coal and shale;
• Classification – Information on the taxonomies used by various groups and organizations;
• Communication – A method to inform professionals, collaborators, and the public about the research conducted within the U.S.G.S. laboratory;
• Research – A database of images related to the characterization of fossil fuel resources in the United States and the world;

What are Macerals:

Macerals are organic matter found within geologic materials (e.g., coal, shale) and are analogous to inorganic minerals. Macerals can contain plant forms and structures or may be degraded to the point that origin cannot be determined. Typically viewed microscopically under reflected light, macerals are divided into three groups:

Vitrinite and Huminite macerals are the coalified remnants of humic materials originating from lignin and cellulose-rich cell walls. Vitrinite and huminite reflectance is used by organic petrologists to determine coal rank (or thermal maturity) and to evaluate the potential for oil/gas production from organic-rich shales.

• Liptinite macerals include hydrogen-rich plant materials such as resins, waxes, and fats as well as spores, pollen and algal material.
• Inertinite macerals are derived from the same sources as vitrinite, huminite and liptinite but have been altered (e.g., through oxidation, fungal attack, charring) and inertinites are relatively higher in carbon and lower in hydrogen content compared to other maceral groups.

Each maceral group is further subdivided into maceral types. View the ASTM or OPTIC Atlases for definitions and labeled photomicrograph examples of maceral types.

Organic petrology also includes the study of secondary organic materials generated during hydrocarbon generation, including solid bitumens.

View the Shale Atlas for labeled photomicrographs of solid bitumens and macerals in shales.

Note: In some cases, maceral identifications labeled in the photomicrographs herein are based on information that may not be apparent in the photographs. For instance, measured reflectance values are used in some cases to make identifications. Such observations sometimes are included in the comments field in photomicrograph metadata.

U.S. Geological Survey Publications Related to the Photomicrograph Atlas 
Gesserman, R.M., Morrissey, E.A., and Hackley, P.C., 2009, Petrographic web atlas for metallurgical bituminous coal macerals: Geological Society of America Abstracts with Programs, Portland, Oregon, October 18-21, 2009, v. 41, no. 7, p. 334. http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_159903.htm 

Valentine, B.J. Morrissey, E.A., Reidy, M.E., Hackley, P.C., 2011, Interactive petrographic web atlas of lignite and subbituminous coals collected from the Gulf Coast region, USA: Program and Abstracts of the 2011 International Committee for Coal and Organic Petrology meeting, Porto, Portugal, September 10-16, 2011, p. 99-100.

Valentine, B.J., Morrissey, E.A., Park, A.J., Reidy, M.E., and Hackley, P.C., 2013, Development of web-based organic petrology photomicrograph atlases and internet resources for professionals and students: International Journal of Coal Geology, v. 111, p. 106-111.

For additional U.S. Geological Survey publications relating to topics within this atlas, please visit the Organic Petrology Publications area of the Energy Resources Program website.

Citation Preference:
Please cite images from the Atlas as follows:

U.S. Geological Survey, 2011, Photomicrograph Atlas: U.S. Geological Survey Energy Resources Program website at https://energy.usgs.gov/PhotoAtlas/default.aspx (Access Date).

[Also see https://coalandcarbonatlas.siu.edu/ from the Crelling's Petrographic Atlas of Coals and Carbons at the Southern Illinois University in Carbondale, Illinois.]