Tourmaline: Properties, Facts and Photos
What is Tourmaline?
The name tourmaline describes a group of more than thirty different minerals. Although they all share a common crystal structure and many physical properties, their chemical composition is not the same.
Considered one of the most complicated groups of silicate minerals, tourmaline occurs in a wide variety of colours and colour combinations.
Vertical striations are a typical characteristic and can often be used to confirm identification.
Striations, which are part of a mineral's crystal habit, are present in several minerals, including pyrite, quartz, and apophyllite. These narrow grooves or ridges often appear as parallel lines. On transparent crystals, they can be mistaken for scratches.
It's common for tourmaline to have fractures and inclusions.
The most common variety of tourmaline is schorl. This mineral is black and typically opaque. Schorl crystals vary in size from very small to very large.
Quartz included with fine crystals of tourmaline is known as tourmalinated quartz.
Dravite is brown tourmaline, although exact shades of colour can vary.
Elbaite is one of the most colourful and well-known varieties. It can occur in almost every colour and can also be bi-coloured or multi-coloured.
Elbaite, which has a lithium-rich composition, often exhibits pleochroism. This optical phenomenon enables different colours to be seen depending on the angle from which the crystal is viewed.
When polished as a cabochon, some varieties of tourmaline can be chatoyant.
Despite the many colours in which tourmaline can be found, its streak is always white.
Rubellite occurs in various shades of red. The name originates from the Latin 'rubellus', meaning 'reddish'. Rubellite and watermelon tourmaline are both varieties of elbaite.
Tourmaline has pyroelectric and piezoelectric properties, meaning it can generate an electric charge in response to heat or mechanical stress.
Flawless crystals can be used in certain electronics, but finding a flawless tourmaline crystal is not easy.
Tourmaline can be found in many countries around the world. Some of the finest crystals come from Africa, the Ural Mountains of Russia, Pakistan, Afghanistan, Sri Lanka, and the U.S.A. The largest deposits are in the Minas Gerais state of Brazil.
Tourmaline grades 7 to 7.5 on the Mohs scale of hardness. Although relatively hard, it's brittle, so will break or fracture easily.
On the Traditional Birthstone Chart, tourmaline is the birthstone for October. On the Modern Chart, opal is October's birthstone, but tourmaline is an alternative.
Article Pictures
The first and third pictures in our article are of Elbaite from Brazil. The second is Schorl. Photos: Courtesy of Stan Celestian.
Pop-up photos
Pyrite, tourmaline, rubellite: Courtesy of Stan Celestian. Dravite: Stone Mania.
