Tourmaline Gemstone
Tourmaline Gemstone
Tanzanite Gemology
Origin Tanzania, Afghanistan, Brazil, East Africa, Nigeria, Mozambique, Madagascar, U.S.A.
Colour Pink, Paraiba, Red, Blue, Orange, Green, blue green, indicolite, rubellite, chrome green, Yellow, Black, Bi color, Tri color, and Fancy colors. Tourmaline can be colorless to just about any color, hue, or tone known to man. Loose tourmaline gemstones come in almost any color
Refractive index 1.624(+.005, -.005) - 1.644(+.006, -.006)
Chemical Composition (NaCa)(LI,MgFe,Al)9B3Si6(O,OH)31
Hardness 7 - 7.5
Density 3.06 (.05, +.15)
Crystal Structure Trigonal
Anniversary 8th year

Tourmaline Information

Tourmaline is the name for a group of related mineral species. In gemological practice, individual species names are not used. Instead all are simply termed "tourmaline." The name is derived from the Sinhalese word "tourmali," which means "mixed parcel."

Color

Color is king for Tourmaline, which is found in more hues, shades and nuances than any other gem. Indeed, not only does tourmaline come in every possible color, but some tourmalines have more than one color in the same stone. Here are a few of the more important varieties:

tourmaline_stone
  • Rubellite - red
  • Indicolite - blue
  • Chrome -intense green coloured by chromium/vanadium
  • Bi-Colour - tourmalines which display two or more colours in the same stone
  • Watermelon - Bi-colour tourmalines which show a green skin and a red core; these are often cut as slices
  • Canary - bright yellow tourmaline from Malawi
  • Paraiba - intense blue to green from Paraiba, Brazil, coloured by copper
  • Cat's Eye - chatoyant tourmaline in a variety of colours
  • Colour-Change - changes from green in daylight to red in incandescent light

Other varieties are sold simply with a colour prefix, as in "pink tourmaline." As with most gems, the colour should be as intense as possible, not too dark or too light.

One of the more distinctive features of tourmaline is its strong pleochroism, with the ordinary ray colour (the colour seen parallel to the c-axis) being deeper than that of the extraordinary ray. In some varieties, this can easily be seen in the face-up position.

Lighting

The proper lighting conditions for tourmaline will depend on the color variety. Reds, oranges and yellows generally look best under incandescent light, while greens, blues and violets appear prettier under daylight. When buying any gem, it is always a good idea to examine it under a variety of light sources, to eliminate future surprises.

Clarity

tourmaline_clearity

Different varieties of tourmaline tend to have different clarities. Thus while large clean tourmalines in the blue and blue-green colors are available, almost all red and pink tourmalines will show eye-visible inclusions. The most common inclusions in tourmaline are fractures and liquid-filled healed fractures. Needle inclusions are also common.

Cut

The cuts used on tourmaline are as varied as the color. Due to its strong pleochroism, darker tourmalines are cut to display the lighter of the two pleochroiccolors. This means orienting the c-axis of the crystal parallel to the table facet. Gems cut with this orientation are often rectangles and rectangular emerald cuts because of the elongated nature of tourmaline crystals.

Tourmalines of lighter color are typically oriented with the table facet perpendicular to the c-axis, to display the richest color possible. Thus they are often cut as rounds, triangles, trillions and ovals. A quick glance at the tourmaline suite shows this.

In addition to faceted stones, cabochon-cut tourmalines are often seen.

tourmaline_cut

Prices

The prices of tourmaline vary tremendously, depending on the variety and quality. Most expensive are the Paraíba tourmalines, which may reach tens of thousands of dollars per carat. Chrome tourmalines, rubellites and fine indicolites and bi-colors may sell for as much as $1000/ct. or more. Other varieties are available for prices between $50-750/ct., depending on the richness of the color.

Stone Sizes

Paraíba tourmalines are extremely rare in faceted stones above 2 cts. Fine Paraíba above 5 carats can be considered world-class pieces. Most stones tend to be less than 1 ct. Chrome tourmalines of quality are rare in sizes above 10 cts., as are rubellites.

Sources

pegmatite-mineral

Tourmaline is a pegmatite mineral and so is mined from the world's great pegmatite districts. Foremost is Brazil, but fine tourmalines are also found in San Diego County, including the famous Pala pegmatite district, and Maine.

The East African countries of Kenya, Tanzania, Mozambique and Madagascar have also produced fine tourmaline in the past. Beautiful yellow "canary" tourmalines come from Malawi, while extremely fine rubellites and blue-green tourmalines are found in Nigeria. Afghanistan, Sri Lanka and Burma also produce gem tourmalines on occasion.

Enhancements

Like the color itself, the enhancement possibilities for tourmaline are wide in variety. The resulting stones are stable under normal wearing conditions and completely safe. Heat treatments are used in some instances, while irradiation is used in others. Occasionally tourmaline is oiled to hide the visibility of fractures and other surface-reaching fissures.

Imitations

Tourmaline has never been synthesized, but a number of imitations exist, including natural stones and man-made imitations such as glass.