Tourmaline
Mineral (Na,Ca)(Mg,Fe,Li,Al)3(Al,Mg)6(Si6O18)(BO3)3(OH)3(OH,F,O)
About it
Group name for long, striated prisms with a rounded triangular cross-section that turn electric when heated or squeezed. Schorl, elbaite, dravite, and the other species are listed separately.
- Type
- Mineral
- Group
- Silicate (cyclosilicate), tourmaline group
- Formula
- (Na,Ca)(Mg,Fe,Li,Al)3(Al,Mg)6(Si6O18)(BO3)3(OH)3(OH,F,O)
- Hardness (Mohs)
- 7–7.5
- Specific gravity
- 2.9–3.3
- Streak
- white
- Lustre
- vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- black, green, pink, red, blue, brown, yellow, colourless, multicoloured
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- indistinct; uneven to conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.