Coal containing more fixed carbon than any other form of coal and the lowest amount of volatile (quickly evaporating) material, giving it the greatest heat value. The most valuable of the coals, it is also the least plentiful, making up less than 2% of all coal reserves in the U.S., with most of the known deposits occurring in the East. Anthracites are black and have a brilliant, almost metallic lustre. Hard and brittle, they can be polished and used for decorative purposes. They are difficult to ignite but burn with a pale-blue flame and require little attention to sustain combustion. In the past they were used for domestic heating, but today they have given way to other sources of energy (e.g., natural gas and electricity).