trigonal Cyclosilicates
Tourmaline (Prismatic)
Formula Complex borosilicate
Crystal Structure
#! Species: Tourmaline
#! System: Trigonal (3m)
#! Habit: Elongated prism with parallel striations
trigonal[3m]:{10-10}@1.0[striation:parallel] + {10-11}@0.8 | elongate(c:2.5)
trigonal
3m
{10-10} {10-11}
Quick Facts
Hardness
7.0
Specific Gravity
3.01
Refractive Index
1.62
Optical Character
Uniaxial -
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 7.0
- Specific Gravity
- 3.01
- Cleavage
- Indistinct
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.62
- Birefringence
- 0.018
- Optical Character
- Uniaxial -
- Dispersion
- 0.017
- Pleochroism
- strong: Dark tone / Light tone (Very strong absorption difference; table should be cut perpendicular to c-axis)
Characteristics
Colours
Pink (Rubellite)RedBlue (Indicolite)Green (Verdelite)YellowOrangePurpleColorless (Achroite)Bi-colorWatermelon (pink core, green rim)Paraíba (neon blue-green)
Localities
BrazilAfghanistanNigeriaMadagascarMozambiqueUSA (California, Maine)
Common Inclusions
Growth tubes parallel to c-axisThread-like inclusionsColour zoningLiquid feathersCrystal inclusions
Known Treatments
Heat treatmentIrradiationFracture filling (rare)
Crystal Forms
prismpinacoiddipyramid
Diagnostic Features
Triangular cross-section; strong pleochroism; parallel striations on prism faces
Synthetics & Simulants
Known synthetic and simulant versions of Tourmaline
Related Minerals
Other minerals in the trigonal system
