trigonal Cyclosilicates
Schorl (Prismatic)
Formula NaFe3Al6(BO3)3Si6O18(OH)4
Crystal Structure
#! Species: Schorl
#! System: Trigonal (3m)
#! Habit: Elongated trigonal prism with 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
3.1
Refractive Index
1.635
Optical Character
Uniaxial -
Physical Properties
- Crystal System
- trigonal
- Hardness (Mohs)
- 7.0
- Specific Gravity
- 3.1
- Cleavage
- Indistinct
- Fracture
- Uneven to conchoidal
- Lustre
- Vitreous to subvitreous
Optical Properties
- Refractive Index
- 1.635
- Birefringence
- 0.02
- Optical Character
- Uniaxial -
- Pleochroism
- strong: Dark brown-black / Lighter brown
Characteristics
Colours
BlackVery dark brown
Localities
Worldwide (most common tourmaline species)BrazilGermanyAfghanistanUSA
Common Inclusions
Growth tubesNeedle inclusions
Known Treatments
None
Crystal Forms
prismdipyramid
Related Minerals
Other minerals in the trigonal system
