Two types of brittle fracture

From triaxial testing at high confining pressures up to 3 GPa and at room temperature, two types of brittle fracture were observed for four dry silicate rocks with low porosity (less than 1%), granite, gabbro, dunite and eclogite ( Chapter 3 ). This suggests that the friction hypothesis for brittle-ductile transition ( Section 3.1.2 ) might not be applicable. In this chapter, we discuss what regimes these types of fracture are placed in, comparing previous experimental results. Other examples of the presence of two types of fracture are shown, which were observed for gneiss at a lower confining pressure and for granite at elevated temperature. The micromechanics of both types are viewed from the standpoint of structural geology.