TOURMALINE(BLUE-GREEN)[GEM]
Listing
description:
Light to dark blue to blue-green tourmaline is also known as Indicolite. Indicolite tourmalines exhibit a
wide range of vivid blue and blue-green shades. Its typical color is a deep
almost neon blue-green.
Detailed description;
History
Brightly
colored Sri
Lankan gem tourmalines were brought to Europe in great quantities by the Dutch East India Company to satisfy a
demand for curiosities and gems. At the time it was not realised that schorl and tourmaline were the same mineral.
Schorl
The
most common species of tourmaline is schorl. It may
account for 95% or more of all tourmaline in nature. The early history of the
mineral schorl shows that the name "schorl" was in use prior to 1400 because a village
known today as Zschorlau (in Saxony, Germany) was then named "Schorl" (or minor variants
of this name). This village had a nearby tin mine where, in
addition to cassiterite, black tourmaline was found. The first
description of schorl with the name "schürl" and its occurrence
(various tin mines in the Saxony Ore Mountains) was written by
Johannes Mathesius (1504–1565) in 1562 under the
title "Sarepta oder Bergpostill". Up to about 1600, additional names
used in the German language were "Schurel",
"Schörle", and "Schurl". Beginning in the 18th century, the
name Schörl was mainly used in the German-speaking area. In English,
the names shorl and shirl were used in the 18th century. In the
19th century the names common schorl, schörl, schorl and iron
tourmaline were used in the Anglo-Saxon area. The word tourmaline has two
etymologies, both from the Sinhalese word turamali, meaning
"stone attracting ash" (a reference to its pyroelectric
properties) or according to other sources "mixed gemstones".
Dravite
The
name dravite was used for the first time by Gustav Tschermak (1836–1927),
Professor of Mineralogy and Petrography
at the University of Vienna, in his book Lehrbuch
der Mineralogie (published in 1884) for magnesium-rich
(and sodium-rich)
tourmaline from the village Unterdrauburg, Drava river area, Carinthia, Austro-Hungarian Empire. Today this
tourmaline locality (type locality for dravite) at the village Dravograd (near
Dobrova pri Dravogradu), is a part of the Republic of Slovenia. Tschermak gave this
tourmaline the name dravite, for the Drava river area, which is the district
along the Drava River (in German: Drau, in Latin: Drave) in Austria and Slovenia. The
chemical composition which was given by Tschermak in 1884 for this dravite
approximately corresponds to the formula NaMg3(Al,Mg)6B3Si6O27(OH),
which is in good agreement (except for the OH
content) with the endmember formula of dravite as known today.
Elbaite
A
lithium-tourmaline (elbaite) was one of three pegmatitic
minerals from Utö, Sweden, in which the new alkali element lithium (Li) was
determined in 1818
by Arfwedson for the first time.[5]
Elba
Island, Italy,
was one of the first localities where colored and colorless Li-tourmalines were
extensively chemically analysed. In 1850 Rammelsberg described fluorine (F) in
tourmaline for the first time. In 1870 he proved that all varieties of tourmaline contain
chemically bound water. In 1889 Scharitzer proposed the substitution of (OH) by F in red
Li-tourmaline from Sušice, Czech Republic. In 1914 Vernadsky proposed
the name Elbait for lithium-, sodium-, and aluminum-rich tourmaline from
Elba Island, Italy, with the simplified formula (Li,Na)HAl6B2Si4O21.
Most likely the type material for elbaite was found at Fonte del Prete, San
Piero in Campo, Campo nell'Elba, Elba Island, Livorno Province, Tuscany, Italy.
In 1933 Winchell published an updated formula for elbaite, H8Na2Li3Al3B6Al12Si12O62,
which is commonly used to date written as Na(Li1.5Al1.5)Al6(BO3)3[Si6O18](OH)3(OH).
The first crystal structure determination of a Li-rich tourmaline was published
in 1972 by Donnay and Barton, performed on a pink elbaite from San Diego County, California, USA.
Physical properties
Crystal structure
Tourmaline
belongs to the trigonal
crystal system and occurs as long, slender to thick prismatic and columnar crystals that are
usually triangular in cross-section. The style of termination at the ends of crystals is
asymmetrical, called hemimorphism. 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.
Color
Tourmaline
has a 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
Treatments
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 (especially paraiba) is worth much less than a
non-treated gem.
Geology
Tourmaline
is found in two main geological occurrences. Igneous
rocks, in particular granite and granite pegmatite and
in metamorphic rocks such as schist and marble. Schorl and
lithium-rich tourmalines are usually found in granite and
granite pegmatite.
Magnesium-rich tourmalines, dravites, are generally restricted to schists and marble. Tourmaline
is a durable mineral and can be found in minor amounts as grains in sandstone and
conglomerate, and is part of the ZTR index
for highly-weathered sediments.
Tourmaline localities
Gem
and specimen tourmaline is mined chiefly in Brazil and Africa. Some placer
material suitable for gem use comes from Sri Lanka. In addition to Brazil,
tourmaline is mined in Tanzania, Nigeria, Kenya, Madagascar, Mozambique,
Namibia, Afghanistan,
Pakistan, Sri Lanka,
and Malawi.[8]
United States
Some
fine gems and specimen material has been produced in the United States, with
the first discoveries in 1822, in the state of Maine. California
became a large producer of tourmaline in the early 1900s. The Maine deposits
tend to produce crystals in raspberry pink-red as well as minty greens. The
California deposits are known for bright pinks, as well as bicolors. During the
early 1900s, Maine and California were the world's largest producers of gem
tourmalines. The Empress Dowager Tz'u Hsi of
China loved pink
tourmaline and bought large quantities for gemstones and carvings from the then
new Himalaya Mine, located in San
Diego County, California.[
It is not clear when the first tourmaline was found in California. Native Americans have used pink
and green tourmaline as funeral gifts for centuries. The first documented case
was in 1890 when Charles Russel Orcutt found pink tourmaline at what later
became the Stewart Mine at Pala,
San Diego.[10]
Brazil
Almost
every color of tourmaline can be found in Brazil, especially in the Brazilian
states of Minas Gerais and Bahia. In 1989,
miners discovered a unique and brightly colored variety of tourmaline in the
state of Paraíba.
The new type of tourmaline, which soon became known as paraiba tourmaline, came
in unusually vivid blues and greens. These colors were often described as
"neon" since they appeared to glow. Brazilian paraiba tourmaline is
usually heavily included. Much of the paraiba tourmaline from Brazil actually
comes from the neighboring state of Rio Grande do Norte. Material from Rio
Grande do Norte is often somewhat less intense in color, but many fine gems are
found there. It was determined that the element copper was
important in the coloration of the stone.
Africa
In
the late 1990s, copper-containing tourmaline was found in Nigeria. The
material was generally paler and less saturated than the Brazilian materials,
although the material generally was much less included. A more recent African discovery
from Mozambique
has also produced beautiful tourmaline colored by copper, similar to
the Brazilian paraiba.
While its colors are somewhat less bright than top Brazilian material,
Mozambique paraiba is often less included and has been found in larger sizes.
The Mozambique paraiba material usually is more intensely colored than the
Nigerian. There is a significant overlap in color and clarity with Mozambique
paraiba and Brazilian paraiba, especially with the material from Rio Grande do Norte. While less expensive than
top quality Brazilian paraiba, some Mozambique material sells for well over
$5,000 per carat, which still is extremely high compared to other tourmalines.
Another
highly valuable variety is chrome tourmaline, a rare type of dravite tourmaline
from Tanzania.
Chrome tourmaline is a rich green color due to the presence of chromium atoms
in the crystal; chromium also produces the green color of emeralds. Of the
standard elbaite colors, blue indicolite gems are typically the most valuable,
followed by green verdelite and pink to red rubellite.
PRICE
$4044781.4/KG OR $1838537/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
website: www.franchiseminerals.com
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