The relative propensity for the different rock types in Australian underground coal mines to ignite methane-bearing atmospheres by frictional contact, either with mining equipment or with other rock materials, has been evaluated by laboratory testing using an instrumented rotating-wheel apparatus. A five-point incendivity categorisation has been developed for the rocks tested, and the results compared to petrographic composition, mineralogy and related chemical properties. Recent experience with ignitions in New South Wales collieries has also been taken into account. With the progressive decline in ignitions from other sources, frictional effects are now the most common source of methane ignition in modern underground coal mines. Conglomerates, lithic or quartzose sandstones with low clay and carbonate contents, and siliceous cherty tuffs appear to represent the most potentially incendive materials in roof and floor strata, along with siliceous or pyritic impregnations that may occur in the coal seam itself. Temperatures in excess of 1500 degreesC may be developed within less than 1 s during rock-on-rock contacts, with ignitions emanating from the contact point or related heat trail rather than from incandescent particles ("sparks") ejected during the friction process. The average temperature and the coefficient of dynamic friction developed during rock-on-rock testing also appear to be related to frictional incendivity characteristics. (C) 2001 Elsevier Science B.V. All rights reserved.