(chemical composition: Ca2(Mg,Fe)5Si8O22(OH)2). Colors: White, light to dark gray, light yellow, light to dark green, light pink to light purple. Rarely colorless; Hardness: 5 to 6; Group: Silicates; Inosilicates; Amphibole group; Formation: Vitreous, silky luster. Sources: Colorado, New York, Connecticut, Italy, Switzerland. Special Notes: Insoluble in acids.