MINERAL IDENTIFICATION KEY METALLIC LUSTER Hardness Cleavage Conchoidal (concave) fracture; variable color; translucent to opaque, Sp. Gr.=2.6 H=7 Harder than glass Cleavage Absent Biotite (mica) hydrous K,Mg,Fe,Al silicate Greasy, talcum-powder feel, waxy-pearly luster various colors, Sp.Gr.2.7; H =1 Talc hydrous K,AL silicate Streak