Tourmaline

The gemstone tourmaline occurs in a wide range of different varieties and color. Tourmalines form in granite and and pegmatite, as well as some metamorphic rocks and alluvial deposits. They are commonly found in association with beryl, feldspar, quartz and zircon.

Top quality tourmalines are among the world’s most precious gemstones. They may be carved into figurines, cut en cabachon, faceted, or sliced into cross-specimens. Some specimens are so beautiful that they need no improvement and are displayed in their natural, uncut state.

Although generally categorized as a distinct mineral, the exact composition of tourmaline is so variable that it is more accurately described as a group. Tourmaline is a hydrous fluoroborosilicate of sodium, calcium, lithium, magnesium, aluminum and ferrous and ferric iron. Within this broad definition there are many different types. This is because several of these chemical elements are interchangeable within the structure of the mineral.

The most valuable tourmaline is elbaite, a lithium-rich form that may appear in a variety of colors. These include achroite (a colorless stone), dravite (colored brown by magnesium), indicolite ( dark blue), and rubellite (red). The black iron-rich variety of tourmaline is known as schorl. Some forms known as watermelon tourmaline, are particolored, with clearly delineated zones of green and pink.

Crystals of tourmaline conform to the trigonal system of symmetry. Externally, they appear in prisms, often with striations. The crystals are pleochroic, so they may appear darker in color when viewed down their long axis then when looked at from the side. This property may be enhanced by judicious cutting.

Although tourmaline crystals are abundant worldwide, only a few occurrences are reported in B.C. Pegmatites at the headwaters of Skookumchuck Creek and St. Mary Lake north of Cranbrook, the Slocan Valley north of Castlegar, and Midge Creek west of Kootenay Lake have reported some tourmaline crystals.

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