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Peridot is the transparent green gem variety of the mineral group known as Olivine.
Peridot is most well known for being the traditional birthstone for the month of August.
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Peridot is a gem variety of the olivine mineral group. The olivines are
isomorphous (all have the same crystal structure), with varying chemical
compositions. The most common of the olivines have chemical compositions
in the complete solid solution series between pure forsterite (Mg2SiO4)
and pure fayalite (Fe2SiO4). A less common solid solution
series also exists between the olivine varieties fayalite (Fe2SiO4) and
Another uncommon solid solution series exists between monticellite (CaMgSiO4)
and kirschteinite (CaFeSiO4). The naturally occurring pure calcium chemical
end member larnite (Ca2SiO4) does not have the olivine structure.
The green color of peridot, the gem variety of olivine, is mainly dependent
on the amount of ferrous iron present, this color then being modified by trace amounts
of Fe3+, Ti4+ and Ni2+. The better green colors occur with a Fe:Mg ratio of
about 1:8. Higher concentrations of Fe result in less desirable yellow-green
or brownish green shades. Pure brown peridots are more rare. Peridot gems
have a hardness of about 6.5, which makes them very suitable for use as
gemstones in peridot earrings and in peridot necklaces, as well as in most other peridot jewelry designs except in rings. The use of peridot gemstones as ringstones
requires some extra care to prevent abrasion and loss of polish.
Peridot (olivine) commonly crystalizes very early in the crystallizing sequence
of mafic and ultra-mafic igneous rocks at relatively high temperatures.
These early formed crystals can settle by gravity forming dunite,
a rock composed essentially of olivine, or the rock known as peridotite which also
contains pyroxene with occaisional accessories hornblende, ilmenite, garnet,
hematite or chromite. Olivine is a common constituent of gabbros and basalts.
Still molten underground basalts, in which early formed peridot grains have
settled to the bottom by gravity, are occaisionally ejected during volcanic
eruptions, and the masses of peridot grains are thrown out as volcanic bombs.
also found as glassy grains in stony meteorites. Mg-rich olivines form by
thermal metamorphism of dolomitic limestones. Fe-rich olivines are less
common, occurring in alkali rocks. Fayalite (Fe2SiO4)
has been found in gas cavities in volcanic rocks and glasses.
Peridot is usually distinguished by its color, luster and conchoidal fracture.
The refractive index and specific gravity of peridot are higher than in
tourmaline, and lower than in chrysoberyl,
zircon and garnet. Sinhalite has a higher specific gravity and more pronounced
pleochrism. Glass and moldavite are isotropic.
The name olivine is from the latin oliva in reference to the mineral's
color. Peridot is from a thirteenth century English word peridote.
From ancient times until the eighteenth century, peridot was referred to
as 'topazion' or 'topaz', most likely because
it was found on the island of Topazios (known today as Zebirget or
Isle of St. John in Egypt) in the Red Sea. In the eighteenth century
the name topaz was given to our mineral topaz of today, and gem olivine became
known as peridot. Yellowish peridot also has been commonly
referred to as chrysolite which is from Greek meaning yellow stone. The
term chrysolite has also been commonly used in refering to greenish-yellow gem chrysoberyl.
Peridot is used as a gemstone. Mg-rich olivine is used in refractory sand and
brick in the casting industry because of its high melting point.
Peridot earrings and other peridot jewelry items are the traditional birthstone gifts for birthdays in the month of August.
The astrological signs of peridot are Virgo, Leo, Libra, Scorpio and Sagittarius.
Peridot is said to bring healing and vitality to the whole body. It is
also said to increase patience, confidence and assertiveness.
Peridot is said to help slow the aging process, and to aid in the
treatment of digestive, heart, lung and eye disorders. It is also said to be helpfull
in facilitating the birthing process.
For more in-depth metaphysical information, see our Metaphysical Books section.
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