Study on the Mechanism of Gas Ignition by Friction Effect of Hard Quartz Sandstone Instability

Table 3

Lithology parameters.

Lithology	Bulk modulus (GPa)	Shear modulus (GPa)	Cohension (MPa)	Internal friction angle (°)	Tensile strength (MPa)	Density (kg·m^-3)
Coal	0.97	0.90	1.10	20	1.34	1300
Sandy mudstone	2.20	1.21	2.10	25	1.83	2340
Siltstone	4.40	2.90	2.50	28	2.18	2696
Fine sandstone	5.87	4.38	3.26	30	3.19	2700
Quartz sandstone	8.06	7.89	5.80	32	4.54	3300