A Series of Precious Stones 6/32

Description

Tourmaline is a crystal silicate mineral compounded with elements such as magnesium , aluminum, iron, sodium, lithium. Tourmaline is classed as a semi-precious stone and the gem comes in a wide variety of colors. The name comes from the Sinhalese word “turamali” or “toramalli”, which applied to different gemstones found in Sri Lanka

Physical Properties :

The style of termination at the ends of crystals is asymmetrical, called hemimorphism It belongs to the trigonal crystal system and occurs as long, slender to thick prismatic and columnar crystals that are usually triangular in cross-section. Small slender prismatic crystals are common in a fine-grained granite called aplite, often forming radial daisy-like patterns. Tourmaline is distinguished by its three-sided prisms; no other common mineral has three sides. Prisms faces often have heavy vertical striations that produce a rounded triangular effect. Tourmaline is rarely perfectly euhedral. An exception was the fine dravite tourmalines of Yinnietharra, in western Australia. The deposit was discovered in the 1970s, but is now exhausted. All hemimorphic crystals are piezoelectric, and are often pyroelectric as well. Tourmaline has variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, while magnesium-rich varieties are brown to yellow, and lithium-rich tourmalines are almost any color: blue, green, red, yellow, pink etc. Rarely, it is colorless. Bi-colored and multicolored crystals are common, reflecting variations of fluid chemistry during crystallisation. Crystals may be green at one end and pink at the other, or green on the outside and pink inside: this type is called watermelon tourmaline. Some forms of tourmaline are dichroic, in that they change color when viewed from different directions. Some tourmaline gems, especially pink to red colored stones, are altered by irradiation to improve their color. Irradiation is almost impossible to detect in tourmalines, and does not impact the value. Heavily-included tourmalines, such as rubellite and Brazilian paraiba, are sometimes clarity enhanced. A clarity-enhanced tourmaline is worth much less than a non-treated gem

Natural Occurrence :

    1. Sri Lanka
    2. South West Africa
    3. Afghanistan
    4. USA (California, Maine)
    5. Brazil
    6. Madagascar
    7. Tanzania
    8. Kenya
    9. UK Rhodesia
    10. Nepal
    11. Mozambique
    12. Pakistan
    13. Namibia and Mexico

Available Colors :

Tourmaline has a variety of colors. Usually, iron-rich tourmalines are black to bluish-black to deep brown, and the other varieties are brown to yellow, and lithium-rich tourmalines are almost any color: red, green, blue, yellow, pink etc.

source:

greatmining (website)