... quartzite, hard slate, chert, basalt, etcHot-Pressed Diamond Drill Bit Hardness & Rock Drillability Grade FormRock Drillability ... , Quartz and Dolomite Marble, Diopside Petrochemical Diorite, Mixed Carbide Powder Rocks, Biotite Hornblende Anorthosite, Pyroxenite through ... Granite.1030-32, 33-35Silicified Marble Rocks, Skarn, Mixed-Plagioclase Gneiss, Albite Porphyry, Feldspar Pegmatite, Amphibolite ...