... specifications as shown below: Hot-Pressed Diamond Drill Bit matrix and Rock Formation Comparison FormEarth PropertyRockBit Matrix TypeSoftShale, soft ... Diorite Porphyry, Black Schist, Diopside Marble Rock, Marble etc.620, 22-25, 26-28Black hornblende Plagioclase Gneiss, White Plagioclase ... , Biotite Dolomite Marble, etc.720, 22-25, 26-28White Plagioclase Gneiss, Quartz and Dolomite Marble, Diopside ...