sedimentary

Possible bituminous coal

Coal, predominantly carbon with macerals and minor mineral impurities

AI-generated identification · may be incorrect

Black to dark gray, irregular and somewhat layered, with a submetallic to dull luster; Mohs hardness about 2–3, noncrystalline, and relatively low density (roughly 1.2–1.5). The photograph is insufficient for definitive identification; it could also be dark shale or slag.

Identified September 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Coal formed from compacted, altered plant material in ancient peat swamps, commonly during the Carboniferous (about 359–299 million years ago), though coal occurs in many ages. Burial, heat, and pressure progressively transformed peat into lignite, bituminous coal, and anthracite.

Uses & applications

Bituminous coal is used for electricity generation, industrial heat, and—when suitable—coke production for steelmaking; attractive pieces may be collected but have little gem value.

Geological facts

A black streak on unglazed porcelain, a relatively light weight, and possible brown-black streak help distinguish coal. It may burn or smell organic when heated, but do not test unknown specimens indoors because of toxic fumes.

Field identification & locations

Common in coal-bearing sedimentary basins worldwide, including the United States, China, Australia, India, and Europe. The specimen’s exact identity requires tests such as streak, density, hardness, and examination of layering.