Glittering Stones >> Semi Precious Stones >> Tourmaline

Semi Precious Stone Tourmaline

The mineral tourmaline is a complex silicate of aluminium and boron, but because of isomorphous replacements it varies widely in composition with iron, magnesium and lithium also entering into the combination to a greater or lesser extent. Tourmaline belongs to the hexagonal system, with long, slender, prismatic acicular crystals that are usually terminated with three faces of a rhombohedron. The smaller crystals are often found in a radial pattern, and collumnar masses are common. The prisms are usually three, six, or nine sided with heavy vertical striations producing a rounded effect. Tourmaline is essentially without cleavage, its fracture is conchoidal to even, its hardness is 7-7.5, its specific gravity is 2.9-3.2, and it has a vitreous lustre inclining to resinous.

Historical Facts of Tourmaline

Refractive index	1.635 – 1.675, 1.610 – 1.650
Chemical Composition	(Ca,K,Na)(Al,Fe,Li,Mg,Mn)3 (Al,Cr,Fe,V)6 (BO3)3 (Si,Al,B)6O18 (OH,F)4
Hardness	7 – 7.5
Crystal Group	Hexagonal
Luster	Vitreous, sometimes resinous
Specific gravity	3.06 (+.20 -.06)
Density	2.82–3.32
Color	Blue, green, red, yellow, pink, brown, orangy red, purplish red, black, colorless
Recognized minerals	Buergerite, Chromdravite, Dravite, Elbaite, Feruvite, Foitite, Liddicoatite, Magnesiofoitite, Olenite, Povondraite, Rossmanite, Schorl, Uvite, Vanadiumdravite
Tourmaline species	Dravite species, Schorl Species, Elbaite Species
Tourmaline varieties	Dravite, Brazilian sapphire, schorl, rubellite variety, indicolite, verdelite or Brazilian emerald, achroite
Occurrence	Brazil, Africa, Sri Lanka, Tanzania, Nigeria, Kenya, Madagascar, Mozambique, Namibia, Afghanistan, Pakistan, Malawi
Pleochroism	Red Tourmaline - Definite; dark red, light red Green Tourmaline - Strong; dark green, yellow-green Brown Tourmaline - Definite; dark brown, light brown Blue Tourmaline - Strong; dark blue, light blue