... , etcCategory: cyclosilicateSize: 10-20mesh 20-40mesh 200mesh 325meshColor: Most commonly black, but can range from brown, violet, green, pink, or in ... elongated. Acicular prisms, sometimes radiating. Massive. Scattered grains (in granite)Crystal systemTrigonalCleavageIndistinctFractureUneven, small conchoidal, brittleLusterVitreous, sometimes resinousStreakWhiteSpecific gravity3.06 (+.20 -.06 ...