trigonal Tectosilicates
Smoky Quartz (Prismatic)
Formula SiO2
Crystal Structure
#! Species: Smoky Quartz
#! System: Trigonal (32)
#! Habit: Hexagonal prism with rhombohedral terminations
trigonal[32]:{10-10}@0.5[striation:horizontal] + {10-11}@1.2 + {01-11}@1.0 | elongate(c:2.0)
trigonal
32
{10-10} {10-11} {01-11}
Quick Facts
Hardness
7.0
Specific Gravity
2.65
Refractive Index
1.544
Optical Character
Uniaxial +
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 7.0
- Specific Gravity
- 2.65
- Cleavage
- None
- Fracture
- Conchoidal
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.544
- Birefringence
- 0.009
- Optical Character
- Uniaxial +
- Dispersion
- 0.013
Characteristics
Colours
Light brownDark brownGreyish-brownNearly black (morion)
Localities
BrazilSwitzerland (Alps)Scotland (Cairngorm)MadagascarUSA (Colorado)
Common Inclusions
Two-phase fluid inclusionsRutile needlesNegative crystals
Known Treatments
Irradiation (to produce or deepen colour)Heat treatment (lightens colour)
Crystal Forms
prismrhombohedron
Diagnostic Features
Brown to black from natural radiation; aluminium colour centres; fades with heat
Related Minerals
Other minerals in the trigonal system
