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.
northern Bowen Basin comprises three coal measures (CM) of the
Blackwater Group, which are termed Moranbah Coal Measures
(MCM), Fort Cooper Coal Measures (FCCM) and Rangal Coal Measures
(RCM) (from bottom to top). These Permian coal accumulations are
known to contain large volumes of coal seam gas (CSG) and are main
exploration targets for CSG production. Further most of the Gondwana coals are ranked as bituminous coals, although anthracites do
occur [6]. A linear decrease of the coal rank was determined to the
north and east of the studied area [7–9].