Physical Properties of Coal (CO-14)
Indiana's bituminous coal is black, but elsewhere lignitic and subbituminous coals are various shades of brown and black. Generally the specific gravity of coal (its weight compared with an equal volume of water) varies with rank and with amount of impurities. The higher the rank and the higher the amount of impurities, the higher the specific gravity. Most Indiana coal has a specific gravity of about 1.3. Hardness of coal varies over a broad range, but knowing this range is important in designing equipment for mining, processing and using coal.
Our Hoosier State Beneath Us: Coal