Tourmaline
Silicate (borosilicate) · complex borosilicate · also: Schorl, Elbaite
Tourmaline is a borosilicate that forms long striated crystals with a rounded-triangle cross-section, ranging from common black schorl to gem multicolours.
What is tourmaline?
Tourmaline is a complex borosilicate best recognised by its elongated crystals with a rounded triangular cross-section and lengthwise striations. Black schorl is common in granites and pegmatites, while gem elbaite comes in pink, green, blue and even “watermelon” crystals with a pink core and green rim. It becomes electrically charged when heated or squeezed.
Properties
- Chemical formula
- complex borosilicate
- Category
- Silicate (borosilicate)
- Hardness (Mohs)
- 7–7.5
- Crystal system
- Trigonal
- Lustre
- Vitreous
- Streak
- White
- Colour
- Black, pink, green, watermelon, blue
- Cleavage / fracture
- None
How to identify tourmaline
- →Long prismatic crystals with lengthwise striations.
- →Cross-section is a rounded triangle (diagnostic).
- →Hardness 7–7.5, no cleavage.
- →Black (schorl) most common; gem colours in pegmatites.
Where tourmaline is found
Fine tourmaline comes from Brazil, Afghanistan, Pakistan, Madagascar and the USA (Maine, California).
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