Anthracite Anthracite Anthracite, often referred to as hard coal, is a hard, compact variety of coal that has a submetallic luster. It has the highest carbon content, the fewest impurities, and the highest energy density of all types of coal and is the highest ranking of coal. Anthracite is the most metamorphosed type of coal (but still represents low-grade metamorphism), in which the carbon content is between 92% and 98%. The term is applied to those varieties of coal which do not give off tarry or other hydrocarbon vapours when heated below their point of ignition. Anthracite ignites with difficulty and
Coal breaker screen (e.g., was of acceptable steam size or smaller). Raw coal often contains impurities such as slate, sulphur, ash (or "bone"), clay, or soil, which requires that it be cleaned before shipment to market. Mine workers sampled the coal as it came out of the mine to determine whether the level of impurity recommended washing (if washing was available). Slate, sulphur, and ash have a higher relative density than coal, and will sink in agitated water. Passing the coal through the tipple was an essential pre-treatment process for coal washing, however, because the impure coal must be of similar sized