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www.mineralgallery.co.za Minerals P-T |
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Tourmaline |
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Name
Tourmaline
Chemistry
Na(Li,Al)3Al6Si6O18(BO3)3 (OH)4, Sodium Lithium Aluminum Boro-Silicate Hydroxide
Uses
As a gemstone
Color
Green to blue to pink.
Hardness
7-7.5
Specific gravity
2.7
Crystals
Trigonal.
Accompanied by:
Rubellite
Fracture
Conchoidal to uneven.
Luster
Vitreous.
Cleavage
Very poor
Streak
White
Similar to:
Aquamarine
Tourmaline is a widespread and abundant complex boron and aluminum silicate minerals Tourmalines form slender, three-, six-, or nine-sided prismatic crystals (hexagonal system) in parallel or radiating groups. Crystal color depends on the composition; black is most common, but brown, green, yellow, red-pink, and blue are also found, and the color may change along the length of the crystal. Some tourmaline crystals are used as semiprecious gems, particularly the blue, red-to-pink, and green crystals, which are also known as Brazilian emeralds. Tourmalines develop an electrical charge when heated or deformed, and pieces cut perpendicular to the long axis can polarize light.
The best-developed Tourmaline crystals are found in granite pegmatites. Crystals are also found in limestones altered by granitic intrusions and, because of high resistance to weathering, in sedimentary deposits.
It is the birthstone for October and the anniversary stone for the 8th year of marriage. Of all the gemstones tourmaline has the widest range of colors. Shades of pink and green are the most common. It is a complicated Aluminum silicate that easily draws to itself impurities. The purest form is the colorless kind. It can have more than one color in the same stone. For example the watermelon tourmaline.
Tourmaline has become probably the best selling 'semi-precious' in recent years. This may partly be due to Paloma Picasso's signature range for Tiffany a few years ago. The enormous variety of colors in which Tourmaline is available was surely a major inspiration for this talented designer. Some of the colors in the group have been give special names such as the red I pink variety known as Rubelite or blue which is known as Indicolite and brown /cognac as Dravite. Green Tourmaline comes in a wide range of shades but the rare Emerald green variety is popularly known as Chrome Tourmaline which relates to the traces of Chromium which give this its unique color. Zambia has been mining Tourmalines for many years - the most famous mine being Hofmeyer Mine near Nyimba. Production there has dropped in recent years but occasionally some fine greens and deep reds are recovered by local diggers at this now abandoned mine. The pink deposits from near Mkushi offer some of the best rubelite we have ever seen in this country and new deposits are constantly being found all over the Eastern Province. Indicolite has been seen but is often mistaken for blue Sapphire by the local dealers whose disappointment is quite obvious at point of sale!
Brazil has been a major producer of Tourmaline for decades and tales of great suffering rewarded by fabulous finds have resounded through the gem trade for many years. Of late however production has dropped due to the exhaustion of some of the most prolific mines.
In the early 90's and extraordinary discovery of bright blue and green tourmaline from Paraiba took the gemworld by storm. Production was slight and most stones recovered weighed less than one gram. Such frenzy ensued to purchase sizeable pieces that in Tuscon's Gem Fair in '92 one +5 ct stone of 'electric / neon 'blue changed hands for a staggering US$8,000 per ct! Namibia has also been a source of fine Tourmalines but again production has dwindled in recent years. Madagascar and Mozambique also have fine Tourmaline deposits. But with the sapphire and Emerald finds in recent years attention has switched to these rarer, more precious stone mines
It is difficult to match colors in the stones due to the fact that colors differ from one stone to the next. It is usually cut into a deep step cut to retain the color of the stone.
Pink tourmaline is commonly known as rubelite, the color ranges from a light pink to a hot deep Fuchsia pink. The green variety is known as verdelite. The deep blue variety is just as scarce and is known as idicolite..
Do not clean your tourmaline in an ultra sound cleaner. We recommend using a soft brush and warm water
