Tourmalines

Elbaite-Albite-Lepidolite-240705
Elbaite-Albite-Lepidolite-240705 (Photo credit: Wikipedia)

Tourmaline, from a Sinhalese word said to mean “stone with mixed colors” or, possibly, “gem pebbles”, is my favorite gemstones for its wide range of colors, especially mixed colors in a single stone, and its beautiful prismatic crystals.

While there are examples of its use in the Ancient World, it was forgotten for many centuries, only being rediscovered in the 17th century through Dutch imports from Sri Lanka where it gained some initial fame as an aschentrekker or “ash-puller”: the stones are often piezoelectric and pyroelectric, developing a charge when heated or under pressure. This property was used to pull ashes from the bowl of a smoker’s pipe. Today, some lighters, including the push-button lighter in a gas grill, use tourmalines to create a spark to light a flammable gas. In World War II, these piezoelectric properties were considered so valuable, tourmaline was declared a strategic resource, used for transducers for depth charges and for early atomic bomb tests.

Elbaite (Paraiba tourmaline - Cuprian Elbaite)...
Elbaite (Paraiba tourmaline – Cuprian Elbaite) – Cut :: Locality: Mavuco, Nampula Province, Mozambique e (Photo credit: Wikipedia)

Like a number of other gemstones (e.g. garnet), Tourmaline is not a specific mineral but a family of minerals with similar crystal forms and properties. Wikipedia lists 25 different minerals in the family, although only two, Liddicoatite and Elbaite, are typically used as gems. Sometimes, the pitch-black variety called schorl is also used as an ornamental stone or makes an interesting inclusion in various rocks polished en cabochon. A brown to orange form, dravite, is also sometimes cut as a gemstone (I picked up a nice set of “savannah” tourmaline a few years ago for my collection for only $20. Love those marketing names 🙂 )

Elbaite, a sodium-rich variety of tourmaline, was first described from a location on the isle of Elba (thus the name). Liddicoatite, named for Richard T. Liddicoate,  has very similar characteristics to Elbaite except that it is calcium rich. Elbaite and liddicoatite form a solid solution series: with pure calcium or sodium at the ends of the series and a mixture of calcium and sodium at intermediate examples.

Watermelon Tourmaline in matrix from Minas Gerais
Watermelon Tourmaline in matrix from Minas Gerais (Photo credit: Wikipedia)

Elbaite comes in a rainbow of colors, green and red being most common, sometimes in the same crystal, which may be red on one end and green on the other; or, more spectacularly, pink in the middle and green on the outside, the famous watermelon tourmaline. Elbaite can also be pink, purple, blue or colorless. Paraiba, Brazil is famous for neon-bright Elbaite due to trace amounts of copper. Cat’s eyes tourmalines are not unknown and some stones show a small amount of color change between natural and artificial lighting (nothing close to the more famous alexandrite, apparently).

In the gem trade, there are names for tourmaline by color, e.g. rubellite, for pink or red Elbaite, but these should not be confused with the mineral names.

Tourmaline often forms beautiful, prismatic crystals, sometimes of exceptional size. The stone is somewhat harder than quartz (7 to 7.5 on the Mohs’ hardness scale, quartz is 7.0) which makes it fairly scratch resistent although its piezo- and pyro-electric tendancies mean it can attract dust and therefore may need frequent cleanings. It typically is fairly pleochroic (different colors perceived on different axis of viewing). Its dispersion is low but as it is valued for its wide range of colors, that only means clear ones don’t make a good diamond substitute. It’s generally modestly priced although emerald-like chrome tourmalines (so named for trace amounts of chromium that provide the color) or ruby-like red can get expensive. The almost neon-bright Paraiba stones are hard to come by these days and can be extremely expensive, though quite striking.

Rubellite Tourmaline Scrollwork Pendant
Rubellite Tourmaline Scrollwork Pendant (Photo credit: Different Seasons Jewelry)

Tourmaline is found in many locations around the world with Brazil being the primary producer of gem material today. In the US, California and Maine are notable for some famous tourmaline mines. Tourmaline, especially green and red, is often used in mid-range jewelry and is a good choice for colored stones for custom jewelry, providing striking color at a fair price.

In the fantasy world, the color-zoning (different colored ends of a prism or different layers of color), can serve as a model for some more unusual gems. Its piezo- or pyroelectric properties could also serve as a ‘false’ source of magic, something used by a trickster pretending to be a wizard. Colored tourmaline prisms could make for striking natural ornamentation in a cave. Or the crystals could serve for a pendant, beautiful wand or staff-crystal, depending on the size.

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2 thoughts on “Tourmalines

  1. Pingback: Garnets: much more than a red gem | M. Q. Allen

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