trigonal Cyclosilicates
Dravite (Prismatic)
Formula NaMg3Al6(BO3)3Si6O18(OH)4
Crystal Structure
#! Species: Dravite
#! System: Trigonal (3m)
#! Habit: Elongated trigonal prism with striations
trigonal[3m]:{10-10}@1.0[striation:parallel] + {10-11}@0.8 | elongate(c:2.0)
trigonal
3m
{10-10} {10-11}
Quick Facts
Hardness
7.0
Specific Gravity
2.98
Refractive Index
1.612
Optical Character
Uniaxial -
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 7.0
- Specific Gravity
- 2.98
- Cleavage
- Indistinct
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.612
- Birefringence
- 0.018
- Optical Character
- Uniaxial -
- Dispersion
- 0.017
- Pleochroism
- strong: Dark brown / Light yellowish-brown
Characteristics
Colours
BrownDark brownYellow-brownOrange-brown
Localities
AustraliaBrazilSri LankaKenyaTanzaniaCanada
Common Inclusions
Growth tubesNeedle inclusions
Known Treatments
Heat treatment (rare)
Crystal Forms
prismdipyramid
Related Minerals
Other minerals in the trigonal system
