Schorl
Mineral NaFe3Al6(Si6O18)(BO3)3(OH)3(OH)
Also called Black tourmaline
About it
Black, deeply striated prisms with a rounded triangular section, the commonest tourmaline; found in granite pegmatites worldwide, with superb crystals from Erongo, Namibia.
- Type
- Mineral
- Group
- Silicate (cyclosilicate), tourmaline group
- Formula
- NaFe3Al6(Si6O18)(BO3)3(OH)3(OH)
- Hardness (Mohs)
- 7
- Specific gravity
- 3.18–3.22
- Streak
- white to bluish white
- Lustre
- vitreous (glassy)
- Crystal system
- Trigonal
- Colours
- black, dark brown, dark blue
- Transparency
- opaque
- Cleavage and fracture
- indistinct; uneven to conchoidal fracture
Typical values: real specimens vary. For more, see mindat.org.