Tourmaline Family

Physical Properties of Tourmaline

Chemical Classification

Boron silicate

Color

Black is the most common color. Also occurs in blue, green, yellow, pink, red, orange, purple, brown, and colorless. Single crystals are often zoned.

Streak

White when softer than the streak plate. Colorless when harder than the streak plate.

Luster

Vitreous

Diaphaneity

Transparent to translucent to nearly opaque

Cleavage

Indistinct

Mohs Hardness

7 to 7.5

Specific Gravity

2.8 to 3.3

Diagnostic

Lack of visible cleavage, prismatic crystals with rounded triangular cross-sections that are often striated, vibrant colors, pleochroism.

Crystal System

Hexagonal

Geologic Occurrence of Tourmaline

Alluvial Tourmaline

Alluvial tourmaline: About 30 carats of stream-rounded tourmaline rough from Tanzania in yellow, orange, and green colors.

Tourmaline as an Accessory Mineral

Accessory tourmaline: A specimen of the Crabtree Pegmatite from North Carolina, showing black prismatic tourmaline and green emerald crystals in a matrix of white feldspar and quartz. The width of this view is about two inches.

Tourmaline Sources

Tourmaline Chemistry

The most common species of tourmaline is schorl. It may account for 95% or more of all tourmaline in nature. The early history of the mineral schorl shows that the name "schorl" was in use prior to 1400 because of a village named "Schorl" in Germany where the black tourmaline was found in a tin mine. It is usually dark brown to black.

Pakistan John A. Betts

Dravite: It is usually dark yellow to brownish black. Power's Farm, Pierrepont, St. Lawrence Co., New York, USA

Maggie Wilson, P. Nicholson

Elbaite species: a sodium, lithium, aluminium boro-silicate, named after the island of Elba, Italy Red or pinkish-red—rubellite variety, Brazil, Knut Eldjarn

Elbaite species Green—verdelite or Brazilian emerald variety, Brazil Antonio Borrelli

Elbaite species, Colorless—achroite variety (from the Greek meaning "colorless"). Afghanistan Rob Lavinsky & irocks.com

Elbaite species Light blue to bluish green—Brazilian indicolite variety (from indigo), Namibia Stephan Koch

Six faceted tourmaline gemstones from Africa. Clockwise from top left: A blue-green oval weighing 5.5 carats; emerald-cut chrome tourmaline, 1.51 carats; green round, 1.87 carats; pink emerald cut, 1.04 carats; pink-orange emerald cut, 1.88 carats; red cushion cut, 3.34 carats. (Photos are not to scale.) Specimens and images copyright by Lapigems.

Names Used for Tourmaline Gems

Color Zoning in Tourmaline

Watermelon tourmaline: rough (left)and faceted (right) tourmalines that exhibit a superb example of watermelon color. Both have clarity problems. This is typical for bicolor tourmaline. Specimens with perfect clarity near the color transition are extremely rare. The change in conditions that caused the color change might have also disrupted the crystal growth to produce the clarity problems. From Minas Gerais, Brazil. The rough crystal measures approximately 4.2 x 1.4 x 1.1 cm, and the faceted gem measures 27.79 mm x 18.51 mm and weighs nearly 50 carats.
Specimens and photos by Arkenstone/www.iRocks.com.

Tourmaline crystal cross-section: A "slice" of watermelon tourmaline which shows the pink interior, green outer layer, and triangular shape of the crystal. This specimen shows the origin of the "watermelon" name.
Image copyright iStockphoto/Sun Chan.

Cat's-Eye Tourmaline

Cat's-Eye Tourmaline: If you look closely you can see the tiny tubes running from left to right within the gem. This wonderful tourmaline is owned by the Edelsteinmuseum (Gemstone Museum) in Idar-Oberstein, Germany and the photo was taken by a photographer who works under the name of Vassil and places many of his photos in the public domain.

Tourmaline Treatments

Imitation Tourmaline

Imitation Tourmaline: An assembled-stone imitation of watermelon tourmaline. It consists of a thin wafer of colored plastic that is glued between two pieces of clear glass and then faceted.

Credits