The coefficient of friction, also called the coefficient of friction, is a dimensionless physical quantity. Between two bodies, the coefficient of friction defines the friction force in relation to the . Its value is required to calculate the friction or friction forceThe coefficient of friction μ is defined as the tangent of the friction angle θ.

Typical values of coefficients of friction for different types of rock:

Class / Coefficient of friction / Associated rock types.

Low friction / 0.36 -0.51 / shale (high mica content), slate, marl.

Medium friction / 0.51 - 0.67 / sandstone, siltstone, chalk, gneiss, shale

High friction / 0.67 - 0.84 / basalt, granite, limestone, conglomerate