Work published by the FRI shows that the relative friability or the relative ease of disintegration of coal, can be measured by its shatter index.
Reference:
Tromp, F. & Bushell, L. 1945. The breakage of South African coal during preparation, haulage and shipping. http://hdl.handle.net/10204/12998 .
Tromp, F., & Bushell, L. (1945). The breakage of South African coal during preparation, haulage and shipping Retrieved from http://hdl.handle.net/10204/12998
Tromp, FJ, and LA Bushell The breakage of South African coal during preparation, haulage and shipping. 1945. http://hdl.handle.net/10204/12998
Tromp F, Bushell L. The breakage of South African coal during preparation, haulage and shipping. 1945 [cited yyyy month dd]. Available from: http://hdl.handle.net/10204/12998