GEMSTONES I LOVE – SOME FACTS ABOUT TOURMALINE

Facts about Tourmaline:

Tourmaline is a crystalline boron-silicate mineral with additional elements such as aluminium, iron, magnesium, sodium, lithium, or potassium. Tourmaline is classified as a semi-precious stone and the gemstone occurs in a wide variety of colors. Tourmaline is actually a group of related varieties rather than a single species. The mineral Elbaite is the member of the Tourmaline group that is responsible for almost all the gem varieties. Tourmaline is the most colorful of all gemstones. Pink, red, green, blue and multicolored are the best known colors. Scientifically, tourmaline is a group of minerals related by physical and chemical properties.  I think my favorite tourmaline jewelry are pieces that display all or many of the colors – like the necklace on the left or the crystal that’s shown later in this article.  Watermelon tourmaline is another of my favorites.

Tourmaline can be opaque or transparent and has a vitreous luster with a hardness of 7-7.5 on the Mohs scale. According to Gemstones of the World, single color crystals are rare – a variety of tones within a single crystal (or even different colors) is more common. The most desirable colors are pink and green. Cat’s eyes are strong only in pink and green hues. Main source of tourmaline is Brazil, but tourmaline deposits are also found in various African and eastern countries. Some deposits also occur in the US.

Heat or pressure can cause a tourmaline crystal to to take an electrical charge (pyro- and piezo-electricity) attracting dust and small particles. As a result, tourmaline needs to be cleaned more often than other gemstones. Heating to higher temperatures can produce color changes in some stones: heating may deepen or lighten colors as can irradiation. Some irradiated stones may fade over time.

When green tourmaline was originally discovered in Minas Gerais Brazil in 1554-55, it was thought to be emerald. According to Secrets of the Gem Trade, “it took three hundred years before the mistake was corrected and ‘Brazilian emerald’ identified as tourmaline. Once found out, tourmaline was shunted aside …until the middle of the twentieth century.”

Minerology distinguishes tourmalines by chemical composition:    1-Paraiba tourmaline is a new variety and color that was discovered in 1989 in the Brazilian state of Paraiba. The color comes from traces of copper and gold in the stone and the primary hues are vivid pastels in the blue-green range. The original mine was quickly exhausted, but similar stone from Australia and elsewhere became available

2-Green tourmaline is the most widely distributed hue and the most common color. There are two varieties of green tourmalines: elbaite (most common and found throughout the world) and chrome tourmaline. The color is due to various impurities. Chrome green tourmaline gets its color from traces of chromium and vanadium.

3-Blue tourmaline historically comes from a couple of mines in Brazil

4-Tourmaline also occurs in pink/red combinations. Watermelon tourmaline has a center core of pink-white with a green outer band

5-Other tourmaline colors – yellow, orange, brown

 

 

Useful references:

Gemstones of the World – Walter Schumann, Sterling Publishing, NY
Secrets of the Gem Trade – Richard W. Wise, Brunswick House Press, Lenox, MA

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