Geology Home Page
Roger Weller, geology instructor
Chemical Group: silicate
Chemical Formula: Na(Mg,Fe)3Al6(BO3)3(Si6O18)(Si6O18)(OH)4
Color: black, brown, dark blue, colorless, pink, red, green, blue and even multicolored
Streak: white Luster: vitreous
Specific Gravity: 3.0 to 3.2
Cleavage: poor Special Properties: strongly pyroelectric and piezoelectric
Crystal Forms: Trigonal
Tourmaline forms long prismatic 3-sided crystals, capped with basal pinacoid.
Crystals are often striated along their lengths.
Mineral Associations: tourmaline is found in pegmatites and metamorphosed rocks.
Identifying Characteristics: rounded triangular cross-section of crystals
Uses: if transparent and colorful, as a gemstone
Occurrences: Brazil; in thee USA from Maine, New Hampshire, South Dakota, California
Toxicity: when-swallowed- low when inhaled- high