Anthracite Coal Pendant Light. Anthracite coal is a sedimentary rock formed as rock strata originating from the Carboniferous. Coal is formed when dead plant matter decays. Through a long process of pressure and heat it eventually forms into the material you have in your hands. Through photosynthesis, it encloses captured carbon present in the atmosphere some 300 million years ago. This particular coal has been sourced in south Wales.