MT6: Minerals with Nonmetallic Luster

Hardness <5.5
Streak that is faint, white or appears white like

Cleavage	Other	Mineral
one	White, gray, apple green in color; pearly luster; greasy feel; may have a slight streak (see also table MT5)	Talc Mg₃Si₄O₁₀(OH)₂
	White in color; satiny or silky luster; fibrous fracture (see also table MT5)	Gypsum CaSO₄ 2H₂O
	Green, blackish green in color; dull, vitreous or pearly luster; may have a faint yellow streak; cleavage flakes are flexible	Chlorite Hydrous Mg-Fe-Al silicate
	Black, brownish black in color; vitreous luster; may have a faint black streak; cleavage surfaces are wavy; transparent; flexible and elastic	Biotite Hydrous K-Mg-Fe-Al silicate
	Colorless, silvery white, brownish silvery white in color; vitreous luster; transparent; flexible and elastic	Muscovite Hydrous K-Al silicate
Two	Black in color; vitreous luster; may have a faint green-gray streak; two perfect cleavages with angles at 124 degrees and 56 degrees; splintery appearance	Hornblende Hydrous Na-Ca-Mg-Fe-Al
Two	Black, dark green in color; vitreous to dull in luster; imperfect cleavages at 90 degrees (see also table MT3)	Augite Ca-Mg-Fe silicate
Three	Clear, gray, red in color; three perfect cleavages at 90 degrees; salty taste	Halite NaCl
	Clear, white, light gray in color; vitreous or pearly luster; brittle sheets; two of the cleavages are poor	Gypsum CaSO₄ 2H₂O
	Colorless, white in color; tabular or rose-like array of crystals; cleavages at 90 degrees	Barite BaSO₄
	Clear, white, possible other colors; vitreous luster; three perfect cleavages form a rhombus; reacts strongly to acid	Calcite CaCO₃
	Buff, gray, white, pinkish in color; small, rhombohedral crystals or massive; three cleavages not at 90 degrees but may be indistinct; reacts slowly with acid or not at all unless powdered (see also table MT5)	Dolomite CaMg(CO₃)₂
Four	Purple, green, blue, yellow, clear in color; vitreous luster; perfect cleavage up to four directions; octahedral cleavage or may occur as cubic crystals	Fluorite CaF₂