The Tourmaline Collection

Tourmaline: Mineralogical Profile

Chemical Formula: $Na(Fe^{2+})_3(Al,Fe^{3+})_6(BO_3)_3Si_6O_{18}(OH)_4$

Physical Properties:

Tourmaline is a complex mineral group characterized by a hardness of 7 to 7.5 on the Mohs scale. It exhibits a white streak and possesses no cleavage. The crystals range from transparent to opaque, typically showing a conchoidal to uneven fracture. The mineral displays a vitreous luster and has a specific gravity ranging from 3.01 to 3.11.

Tourmaline exhibits weak fluorescence, displaying a wide range of colors under ultraviolet light, including colorless, blue-green, yellow, greenish-blue, weak red, reddish-purple, pink, brown, green, and blue.

Chemical Composition & Classification:

Tourmaline is not a single mineral but a complex group of related borosilicate minerals containing aluminum, magnesium, and iron. Its chemical composition varies significantly based on its constituent cations. In mineralogy, tourmaline is classified into distinct species based on these chemical variations, including:

• Elbaite: The lithium-rich species.


• Schorl: The iron-dominant species.


• Dravite: The magnesium-rich species.


• Uvite: A magnesium-calcium species.


• Buergerite: An iron-rich species.


• Tsilaisite: The manganese-rich species.

Note: While these scientific classifications define the mineral species, in the commercial gem market, tourmalines are often identified and traded primarily by their color rather than their specific mineralogical species.