Dravite
Mineral NaMg3Al6(Si6O18)(BO3)3(OH)3(OH)
Also called Brown tourmaline
About it
Brown magnesium tourmaline of marble and schist, in stubby crystals; Yinnietharra in Western Australia and Brumado in Brazil are known, and it occurs in Ontario's Grenville marbles.
- Type
- Mineral
- Group
- Silicate (cyclosilicate), tourmaline group
- Formula
- NaMg3Al6(Si6O18)(BO3)3(OH)3(OH)
- Hardness (Mohs)
- 7–7.5
- Specific gravity
- 3.03–3.18
- Streak
- white to pale brown
- Lustre
- vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- brown, yellow-brown, dark brown, black, green
- Transparency
- transparent, translucent, opaque
- Cleavage and fracture
- indistinct; uneven to conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.