Transparent Gems
- Author Joseph Kieffer
- Published February 9, 2011
- Word count 1,261
The transparent gems are known for their striking luster and brilliance
along with their color and hardness. Most transparent gems are oxides of
aluminum, beryllium, or magnesium, with a few containing silica. Some
transparent gems such as ruby and sapphire are identical in mineral composition
and only differ in color. The value of these stones is determined
largely by their transparency, lack of flaws, brilliancy of color, and size.The
corundum gems, including ruby and sapphire, are all rare forms of alumina
(Al2O3) that vary widely in color. Green, purple, and yellow corundum are
known as oriental emerald, oriental amethyst, and oriental topaz. In addition,
synthetic rubies, sapphires, emeralds, and similar gems of large size and
fine quality are made by fusing fine alumina with appropriate mineral pigments
under high temperatures.
Ruby is the most valued of all gemstones, and the deep red varieties
are prized even more than diamonds. It is a vivid red gem of the mineral
corundum, which is second in hardness to diamond on the Mohs’ hardness
scale.The color, attributed to the presence of a small amount of chromium,
varies from deep red to pale rose red, and in some stones it shows a tinge
of violet. The oriental ruby, mined mostly in Burma, has very limited
distribution, which accounts for its extraordinary high value. The ruby
was considered by the Hindus the king of the precious stones. It was
also thought to bestow good fortune when worn on the left side of the
body.
Sapphire is the serene blue variety of corundum and is essentially the
same mineral as ruby, differing only in color and being slightly harder. It also
occurs in vivid green, violet, and yellow hues.The color of the ever-popular
rich blue sapphire is attributed to the presence of oxides of chromium, iron,
or titanium.The Montana variety has a peculiar electric blue color. Star sapphires
are unusual in that they reflect light in a figure of a six-pointed star.
Emerald, known for its deep green color, is a gem of the mineral beryl
and should not be confused with the oriental emerald, which is actually an
emerald-colored sapphire. Beryl is an important ore of beryllium as well as a
major gemstone.The crystals are hexagonal and are principally found in granite
pegmatites. When colored green, beryl is emerald, when colored blue or
blue-green it is aquamarine, and when colored pink it is morganite. Emerald
colors vary from light green to dark green and are due to the presence of
chromium. Compared to the other transparent gems, the emerald is relatively
soft, only slightly harder than quartz. Emeralds were mined in Egypt as early
as 1650 B.C., and Cleopatra’s mines, located on the Red Sea coast east of
Aswan, yielded precious emerald gems to adorn the queen of Egypt. Emeralds
were once thought to have therapeutic value, curing such afflictions as poisoning,
diseases of the eye, and the possession of demons.
Zircon is one of the most extraordinary gems. It is fairly common
in igneous rocks, but rare as a gemstone. Zircon crystals found in granite
are enormously resistant to erosion and tell of the earliest history of the
Earth, when the crust first formed some 4.2 billion years ago.
Zircon is also an important ore for zirconium, hafnium, and thorium. A rich golden brown
variety is the most magnificent of all gemstones possessing this color. The
natural colors range from clear varieties, which are favorite substitutes for
diamonds, through shades of yellow and brown to deep brownish red. Brown
zircon crystals can be altered to a rich blue variety by heating them in the
absence of air, a potential that makes them more highly prized gems.
Tourmaline, often called the "rainbow gem," displays the widest range of
exquisite colors of all the gems.The crystals are often long and are unique in
having curved triangular cross sections. Not only does tourmaline appear in
almost every color of the rainbow, but a single crystal might be half one color
and half another or show three different colors resembling a candy cane.The
profusion of colors is due to a complex chemical composition, including perhaps
a greater variety of chemical elements than any other mineral.The most
valuable colors are a clear ruby red and a bright sapphire blue.Tourmaline is
very common in pegmatites, where it sometimes occurs in crystals of enormous
size. Because of its unique crystal structure, tourmaline has a
strange electrical property. It becomes positively charged at one end and negatively
charged at the other end of the crystal when heated. The static electricity
attracts such objects as small bits of paper similarly to the way a comb
drawn through the hair does.
Garnet is a rare gem of silicates of various metals with a typically red,
brown, yellow, white, green, or black color and a glassy to resinous luster.
Garnets are a common group of closely related silicate minerals, containing
calcium, magnesium, iron, and aluminum, combined with silicon and oxygen.
Crystals are usually 12- or 24-sided or any combination to yield 36 and 48
sides. Demantoid is a brilliant green variety that resembles an emerald in
color. Pyrope, sometimes called precious garnet, is deep red and used in jewelry.
Perfect specimens are found in South African "blue earth" in kimberlite
pipes associated with diamonds and make exceedingly fine gems.
Staurolite is an iron-aluminum silicate often found with garnets in metamorphic
rocks such as schists, phyllites, and gneisses and in pegmatites. An
unusual inclusion of staurolite mineral in a South African diamond implies
that it came from a piece of continental crust that was recycled through the
mantle. Staurolite is brown to black and almost always occurs as stubby prismatic
crystals usually an inch or less long, but in excellent specimens they are
up to two inches long.Twinning is common, and when occurring at right
angles the twin crystals form a perfect cross. These crystals, called
fairy crosses, are broken or weathered from the bedrock and are sold as charms
or souvenirs.Transparent crystals are rare and are cut as gemstones.
Peridot is a clear yellow-green gem of the mineral olivine, which is the
most common member of a group of silicates found in many igneous rocks.
It is an iron-magnesium silicate and the simplest of the dark minerals. Olivine
is found in igneous rocks rich in magnesium and low in quartz such as basalt
and gabbro. It has small, sugary grains, and crystals are relatively rare, although
occasionally some up to several inches long have been found. Peridotite is the
rock name for this mineral, which is significant because a very similar rock
type is mined from volcanic structures called kimberlites for diamonds, indicating
the mineral originated within the Earth’s mantle.
Topaz is commonly a yellow gemstone but ranges in color from pale yellow
to brown. It has been very popular for jewelry since the 16th century.The
rare pink topaz is much admired, especially the deeper hues. Topaz has a
remarkably slick surface and a slippery feeling that distinguishes it from other
minerals. Some large crystals, weighing upward of 600 pounds, have been
found in pegmatites, with colors varying from yellow to blue, green, violet,
and colorless.The yellow, yellow-brown, and blue-green varieties often occur
in beautiful crystals that make valuable gems.The most important commercial
source of the gemstone is Brazil.The mystical powers of topaz are believed to
increase when the moon is new or full in the sign of Scorpio, at which time
the wearer is able to receive strong impressions from astral sources.
Joseph Kieffer from society http://jewelryuk.org
from: http://hand-crafted-jewelry.com
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