Information
INTRODUCTION TOURMALINE
Tourmaline Gem is a semi-precious mineral, with colors ranging from magenta to teal-blue, meadow-green to vibrant yellow, and even black.
In old Egyptian legend, tell us, 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’
COLOR, CLARITY AND CUT
This gem is in fact, one of the most interesting. It exists in a wide range of colours each with its own name, as follows
Achroite – colourless
Chrome Tourmaline- green, containing chromium;may be mistaken for emerald
Dravite – brown
Indicolite – Blue;has been passed off as Sapphire.The yellow variety from Kenya has been sold as Yellow Sapphire,
Rubellite – red;in the deeper shades has been mistaken for Ruby.
Schorl – black;was used for mounting jewellery
Other Varieties – green is the most common colour ande ranges in shade from very pale to dark.A new variety was discouvered in Brazil in 1987 that is a transparent ,intense blue or bluish green.These are known as Paraiba or Neon Tourmaline and command extremely high prices.
Pariaba is the are in Brazil where it was originally discovered and it owes its outstanding colour to the presence of copper in its makeup.A similar colour tourmaline has subsequently been discouvered in Nigeria and Madagascar,both containing copper but to a lesser amount than the Brazilian.They are consequently cheaper.Initially these gems were called ‘Paraiba’,though the correctness of this term is still hotly debated.In the meantime terms like ‘Paraiba type’ or ‘cuprian tourmaline’ or even ‘cuprian elbaite tourmaline’ are being used.
Sometimes crystals form where the colours are in layers around the length of the crystal.In some the centre is pink and the outer green with a colourless layer in between.When a cross-section of the crystal is cut it is known as Watermelon Tourmaline.Very attractive ,but also expensive.
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.
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 pleochroic colors. 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. Paraiba tourmalines are extremely rare in faceted stones above 2 cts. Fine Paraiba 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.
VALUE
The value of tourmaline it is 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. Visit our dubai online shopping and we can assist you with the right information about the value of Tourmaline and about any other gold stones.
PROPERTIES OF TOURMALINE
| Composition | Tourmaline is one of the most complex of all mineral groups, and includes the following species: • Buergerite: NaFe3+3Al6(BO3)3Si6O18(O)3(OH) • Chromdravite: NaMg3[Cr,Fe3+]6(BO3)3Si6O18(OH)4 • Dravite: NaMg3Al6(BO3)3Si6O18(OH)4 • Elbaite: Na(Li1.5Al1.5)Al6(BO3)3Si6O18(OH)4 • Feruvite: CaFe2+3[Al5Mg](BO3)3Si6O18(OH)4 • Foitite: [Fe2+2(Al,Fe3+)]Al6(BO3)3Si6O18(OH)4 • Liddicoatite: Ca(Li2Al)Al6(BO3)3Si6O18(OH)4 • Magnesiofoitite: [Mg2+2(Al3+)]Al6(BO3)3Si6O18(OH)4 • Olenite: NaAl3Al6(BO3)3Si6O18(O)3(OH) • Povondraite: NaFe3+3Fe3+6(BO3)3Si6O18(O)3(OH) • Rossmanite: (LiAl2)Al6(BO3)3Si6O18(OH)4 • Schorl: NaFe2+3Al6(BO3)3Si6O18(OH)4 • Uvite: CaMg3[Al5Mg](BO3)3Si6O18(OH)4 In summary, tourmaline is a complex aluminum boro-silicate, with heavy emphasis on the “complex.” One pundit likened it more to a medieval alchemist’s brew than a respectable mineral species. And a glance at the above formulae would bear that out. |
| Hardness (Mohs) | 7 to 7.5 |
| Specific Gravity | 3.06 (+ 0.20; – 0.06) |
| Refractive Index | 1.624–1.644 (0.18–0.40; usually 0.20, may be greater in dark stones); doubly refractive, uniaxial negative |
| Crystal System | Hexagonal-trigonal |
| Colors | Any and all. Tourmaline occurs in more colors than any other gem. Some colors have specific variety names, including: • Bi-color: More than one color in the same stone • Chrome: Intense green, colored by chromium and/or vanadium • Indicolite: Blue • Paraíba: Electric blue to green, colored by copper • Rubellite: Red • Watermelon: Pink in the center, green at the edge |
| Pleochroism | Strongly dichroic with the ordinary ray having a darker color |
| Dispersion | 0.017 |
| Phenomena | Cat’s eye tourmalines are common. Color-change chrome tourmalines, which change from green to red, are occasionally found. |
| Handling | Ultrasonic: generally safe, but risky if the gem contains liquid inclusions Steamer: not safe The best way to care for tourmaline is to clean it with warm, soapy water. Avoid exposing it to heat or acids. |
| Enhancements | A variety of enhancements are regularly applied to tourmaline, depending on the source and variety. These include heat, irradiation, and oiling. |
| Synthetic available? | No |
ORIGIN AND IMITATION
Tourmaline occurs in Brazil ,Russia, the USA ,Africa, India, Pakistan and Sri Lanka .Like quartz, tourmaline displays pyroelectric effects (upon heating, an electric charge is induced with opposite polarity at each end of the crystal) and piezoelectric effects(when under pressure an electrical charge is induced)
Tourmaline has never been synthesized, but a number of imitations exist, including natural stones and man-made imitations such as glass.
NAME, FAME AND LEGEND
Tourmaline he gets his name from the Singhalese phrase “tura mali,” which means, “stone mixed with vibrant colors.”Richard Keene he write in his article in San Diego ‘s Casket about a legend regarding the tourmaline. Once upon a time there lived a hideous evil spirit, who being himself so ugly, was thrown into a terrible rage on seeing anything beautiful. One day while sitting on the edge of the cave in which he lived, he saw a rainbow in the sky above him, and on seeing its varied and beautiful colors, his anger knew no bounds. By the use of an evil spell he captured the many-hued rainbow and carried it into the dark fissure, where it remained unto this day, and prospectors finding pieces of the broken rainbow, crushed by this evil spirit in his fury, named them tourmaline.
