Anthracite is only mined in eastern Pennsylvania. It occurs in the form of laminates in rock formations, it specific gravity, solubility, and hardness are variable and in relation to the impurities found with it. Some research has shown that these impurities contribute to friability along the cleavage planes. Experience has shown coal having Specific Gravity - 1.60-1.70; Acid Solubility - less than 2%; MOH Hardness greater than 3; Carbon Content greater than 80% (dry basis) is more resistant to size reduction because its density and hardness come from the number of carbon to carbon bonds rather than from its inherent rock. |
