trigonal Tectosilicates
Quartz (Amethyst Geode (druse))
Formula SiO2
Crystal Structure
#! Species: Quartz (amethyst)
#! System: Trigonal (32)
#! Habit: Druse lining of ~50 crystals
trigonal[32]:{10-10}@1.0 + {10-11}@0.8 ~ druse[50]
trigonal
32
{10-10} {10-11}
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
- Pleochroism
- None (in colourless)
Characteristics
Colours
Colourless (rock crystal)White (milky)Various (see variety gemstones)
Localities
BrazilMadagascarUSAAlpsWorldwide
Common Inclusions
Two-phase fluid inclusionsNegative crystalsRutile needlesTourmaline crystalsVarious mineral inclusions
Known Treatments
Heat treatmentIrradiationCoating
Crystal Forms
prismrhombohedrondruse
Diagnostic Features
Conchoidal fracture; lacks cleavage; hexagonal cross-section with horizontal striations on prism
Notes
Aggregate druse lining; classic presentation for amethyst from Brazil and Uruguay
Synthetics & Simulants
Known synthetic and simulant versions of Quartz
Related Minerals
Other minerals in the trigonal system
