Tourmaline

Tourmaline is a crystal silicate mineral compounded with elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word "Thuramali" or "Thoramalli" which applied to different gemstones found in Sri Lanka.

Tourmalines are gems with an incomparable variety of colours. The reason, according to an old Egyptian legend, is that the tourmaline, on its long journey up from the centre of the Earth, passed over a rainbow. In doing so, it assumed all the colours of the rainbow. And that is why it is still referred to as the 'gemstone of the rainbow' today.

Tourmaline is borosilicate mineral of complex and variable composition. Tourmaline is very abundant and has the best-developed crystals in pegmatites and in metamorphosed limestones in contact with granitic magmas. The colored varieties, when transparent and free from flaws, are cut as gems. Transparent crystals of tourmaline are dichroic - the depth of color varies as the crystal is turned in the light. Another peculiarity of tourmaline is that crystal when heated acquires an electric charge and attracts small objects such as hair or small pieces of paper. Rubbing crystal imparts a similar charge.

Brightly colored Sri Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a demand for curiosities and gems. At the time it was not realized that schorl and tourmaline were the same mineral.

More About Tourmaline Varieties

The tourmaline group refers to a number of related species and varieties. The names commonly used in the gems business -- names like paraiba, rubellite and indicolite -- are actually trade names, not gemological names.

The gemological names identify the different tourmaline varieties according to their chemical composition, not their color. This is the same convention used in the garnet group, where the term andradite, for example, is used to pick out the calcium iron silicates in the garnet family.

Most of the tourmaline you'll find sold as gemstones is Elbaite, a lithium rich tourmaline that occurs in transparent and translucent crystals in a wide range of colors. Elbaite is named after the island of Elba in Italy, famous as the site of Napoleon's exile after his forced abdication in 1814.

The other variety of tourmaline that is commonly found is schorl, an iron rich tourmaline that is an opaque black. Schorl is widely available -- it accounts for more than 90% of the tourmaline in nature -- and inexpensive, but is popular as a gemstone since it takes a good polish.

The less common tourmaline varieties include buergerite, dravite, liddicoatite and uvite. Buergerite, named after the MIT mineralogist Martin Buerger, is an iron-rich tourmaline that occurs in bronze, brown and black. Dravite is a magnesium tourmaline that is dark yellow to brownish black in color. It is named after the Drava river area of what is now Slovenia.

Liddicoatite is a calcium tourmaline, named in honor of Richard Liddicoat, the GIA gemologist who invented the diamond grading system. It is found in a range of colors, include blue, brown, green, pink and red.

Uvite is an magnesium/iron-rich tourmaline that was named after a province in Sri Lanka. It is usually dark green to black in color. One of the unusual features of uvite is that it tends to form stubby crystals rather than long prismatic crystals like most other tourmalines.