Coal (frae the Auld Inglis term col, which haes meant "mineral o fossilised carbon" syne the 13t century) is a combustible black or brounish-black sedimentary rock uisually occurrin in rock strata in layers or veins cried coal beds or coal seams. The haurder forms, such as anthracite coal, can be regairdit as metamorphic rock acause o later exposur tae elevatit temperature an pressur. Coal is componed primarily o caurbon alang wi variable quantities o ither elements, chiefly hydrogen, sulfur, oxygen, an nitrogen.
- Harper, Douglas. "coal". Online Etymology Dictionary.
- Blander, M. "Calculations of the Influence of Additives on Coal Combustion Deposits" (PDF). Argonne National Laboratory. p. 315. Retrieved 17 December 2011.