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 :
Sri Lanka
South West Africa
Afghanistan
USA (California, Maine)
Brazil
Madagascar
Tanzania
Kenya
UK Rhodesia
Nepal
Mozambique
Pakistan
Namibia and Mexico