Coal is a heterogeneous material, which fractures naturally [1]
and its properties are related to its lithotype (organic composition), rank (thermal maturity) and grade (mineral matter content)
[2]. Therefore it is important to sample for these differences in any
study of surface hardness to determine predictive relationships
between these parameters. These relationships can also relate to
fracture toughness and strength, which are useful factors for coal
drillability, fracture stimulation, breakage and grindability.
Surface hardness is a physical property of rocks and can be
tested using a Shore Scleroscope Rebound Hardness (SSRH) tester,
a low budget method, which has been accepted as a nondestructive and convenient technique for rock hardness estimation
[3]. The “Rebound Hardness Tester” from IMAI SIKENKI CO., LTD.,
Tokyo (Nov. 1970, No. 70756) has been employed in this study.