Anthracite coal is the highest grade of coal. Anthracite is dark black, very shiny and has a glass like consistency. In the United States the primary source is Northeastern Pennsylvania. It has an average BTU content of 24 to 25 million per ton but can exceed 28 million for the highest quality anthracites.
Anthracite has very high carbon content that will range from about 85 or 95 percent. It burns with a bright blue flame similar to what you would expect from natural gas. It also has a low ash and low sulfur content. These characteristics and others make it ideal for a home heating fuel even if the heating unit is placed directly in the living space.
The primary use for anthracite is as a home heating fuel, other uses include water filtration, as a coking product and other industrial uses. Compared to bituminous coal anthracite has some very distinct advantages for home heating. Because of the low volatile content it will burn up to fine powdery ash. Ashes from stokers or if the coal has been over-fired may have some ash with a granola like texture that easily crumbles in your hands.
Anthracite's high cost relative to bituminous coal make it very expensive as thermal coal for power plants and has very little use for that industry. Those higher costs are because it's more expensive to mine and because of it's characteristics it's a much more desirable product.