Is anthracite available with a MOH hardness greater than 3.5?
Testing for Moh’s hardness is not an exact science. “Standard” materials are not homogeneous, and therefore a sample that scratches the “standard” in one lab may not in another. In addition, the scale’s increments are not uniform. Fractional values such as 2.7 or 3.5 must be achieved using statistical methods that differ from lab to lab. Coal that repetitively scratches a copper penny, (approximate Moh’s hardness of 3) and exhibits the other characteristics of quality anthracite as stated above, has been shown repeatedly to be more durable, and to perform longer than coal of lower Moh hardness.
