Turquoise
Turquoise is an opaque, blue-to-green
mineral that is a
hydrous phosphate of
copper and
aluminium, with the
chemical formula CuAl6(
PO
4)
4(
OH)
8·4
H
2O. It is rare and valuable in finer grades and has been prized as a
gem
and ornamental stone for thousands of years owing to its unique hue. In
recent times, turquoise, like most other opaque gems, has been devalued
by the introduction of treatments, imitations, and synthetics onto the
market.
The substance has been known by many names, but the word
turquoise, which dates to the 16th century, is derived from an
Old French word for "Turkish", because the mineral was first brought to Europe from
Turkey, from the mines in historical
Khorasan Province of
Iran.
[2][3][4][5] Pliny the Elder referred to the mineral as
callais, the Iranians named it "phirouzeh" and the
Aztecs knew it as
Teoxihuitl.
[4]
Properties of turquoise
Even the finest of turquoise is fracturable, reaching a maximum
hardness of just under 6, or slightly more than window glass.
[2] Characteristically a
cryptocrystalline mineral, turquoise almost never forms single
crystals and all of its properties are highly variable. Its
crystal system is proven to be
triclinic via
X-ray diffraction testing. With lower hardness comes lower
specific gravity (2.60–2.90) and greater
porosity: These properties are dependent on grain size. The
lustre of turquoise is typically waxy to subvitreous, and
transparency
is usually opaque, but may be semitranslucent in thin sections. Colour
is as variable as the mineral's other properties, ranging from white to a
powder blue to a sky blue, and from a blue-green to a yellowish green.
The blue is attributed to
idiochromatic copper while the green may be the result of either
iron impurities (replacing aluminium) or
dehydration.
The
refractive index (as measured by
sodium light, 589.3 nm) of turquoise is approximately 1.61 or 1.62; this is a mean value seen as a single reading on a
gemmological refractometer, owing to the almost invariably polycrystalline nature of turquoise. A reading of 1.61–1.65 (
birefringence 0.040, biaxial positive) has been taken from rare single crystals. An
absorption spectrum may also be obtained with a hand-held
spectroscope,
revealing a line at 432 nanometres and a weak band at 460 nanometres
(this is best seen with strong reflected light). Under longwave
ultraviolet light, turquoise may occasionally
fluoresce green, yellow or bright blue; it is inert under shortwave ultraviolet and
X-rays.
Turquoise is insoluble in all but heated
hydrochloric acid. Its
streak is a pale bluish white and its
fracture is
conchoidal,
leaving a waxy lustre. Despite its low hardness relative to other gems,
turquoise takes a good polish. Turquoise may also be peppered with
flecks of
pyrite or interspersed with dark, spidery
limonite veining.
Formation
As a secondary
mineral, turquoise apparently forms by the action of percolating acidic aqueous solutions during the
weathering and
oxidation of pre-existing minerals. For example, the copper may come from primary copper sulfides such as
chalcopyrite or from the secondary carbonates
malachite or
azurite; the aluminium may derive from
feldspar; and the phosphorus from
apatite. Climate factors appear to play an important role as turquoise is typically found in
arid regions, filling or encrusting cavities and fractures in typically highly altered
volcanic rocks, often with associated
limonite
and other iron oxides. In the American southwest turquoise is almost
invariably associated with the weathering products of copper sulfide
deposits in or around potassium feldspar bearing porphyritic
intrusives. In some occurrences
alunite,
potassium aluminium sulfate, is a prominent secondary mineral.
Typically turquoise mineralization is restricted to a relatively shallow
depth of less than 20 metres (66 ft), although it does occur along
deeper fracture zones where secondary solutions have greater penetration
or the depth to the water table is greater.
Although the features of turquoise occurrences are consistent with a secondary or
supergene origin, some sources refer to a
hypogene origin. The
hypogene hypothesis holds that the aqueous solutions originate at significant depth, from
hydrothermal
processes. Initially at high temperature, these solutions rise upward
to surface layers, interacting with, and leaching essential elements
from pre-existing minerals in the process. As the solutions cool,
turquoise precipitates, lining cavities and fractures within the
surrounding rock. This hypogene process is applicable to the original
copper sulfide deposition; however, it is difficult to account for the
many features of turquoise occurrences by a hypogene process. That said,
there are reports of two phase
fluid inclusions within turquoise grains that give elevated homogenization temperatures of 90 to 190 °C that require explanation.
Turquoise is nearly always cryptocrystalline and massive and assumes
no definite external shape. Crystals, even at the microscopic scale, are
exceedingly rare. Typically the form is vein or fracture filling,
nodular, or botryoidal in
habit.
Stalactite forms have been reported. Turquoise may also
pseudomorphously replace feldspar, apatite, other minerals, or even
fossils.
Odontolite is fossil bone or
ivory that has been traditionally thought to have been altered by turquoise or similar phosphate minerals such as the iron phosphate
vivianite. Intergrowth with other secondary copper minerals such as
chrysocolla is also common.
Occurrence
Turquoise was among the first gems to be mined, and while many
historic sites have been depleted, some are still worked to this day.
These are all small-scale, often seasonal operations, owing to the
limited scope and remoteness of the deposits. Most are worked by hand
with little or no mechanization. However, turquoise is often recovered
as a byproduct of large-scale copper mining operations, especially in
the United States.
Cutting and grinding turquoise in
Nishapur, Iran, 1973
Iran
For at least 2,000 years, Iran, known before as
Persia,
has remained an important source of turquoise which was named by
Iranians initially "pirouzeh" meaning "victory" and later after Arab
invasion "firouzeh".
[citation needed]
In Iranian architecture, the blue turquoise was used to cover the domes
of the Iranian palaces because its intense blue colour was also a
symbol of heaven on earth.
[citation needed]
This deposit, which is blue naturally, and turns green when heated
due to dehydration, is restricted to a mine-riddled region in
Nishapur, the 2,012-metre (6,601 ft) mountain peak of
Ali-mersai, which is tens of kilometers from
Mashhad, the capital of
Khorasan province,
Iran. A weathered and broken
trachyte is host to the turquoise, which is found both
in situ between layers of limonite and sandstone, and amongst the
scree at the mountain's base. These workings, together with those of the
Sinai Peninsula, are the oldest known.
[5]
Sinai
Since at least the
First Dynasty (3000
BCE), and possibly before then, turquoise was used by the
Egyptians and was
mined by them in the
Sinai Peninsula, called "Country of Turquoise" by the native
Monitu.
There are six mines in the region, all on the southwest coast of the
peninsula, covering an area of some 650 square kilometres (250 sq mi).
The two most important of these mines, from a historic perspective, are
Serabit el-Khadim and
Wadi Maghareh,
believed to be among the oldest of known mines. The former mine is
situated about 4 kilometres from an ancient temple dedicated to
Hathor.
The turquoise is found in sandstone that is, or was originally, overlain by
basalt.
Copper and iron workings are present in the area. Large-scale turquoise
mining is not profitable today, but the deposits are sporadically
quarried by
Bedouin peoples using homemade
gunpowder. In the rainy winter months, miners face a risk from
flash flooding;
even in the dry season, death from the collapse of the haphazardly
exploited sandstone mine walls is not unheard of. The colour of Sinai
material is typically greener than Iranian material, but is thought to
be stable and fairly durable. Often referred to as
Egyptian
turquoise, Sinai material is typically the most translucent, and under
magnification its surface structure is revealed to be peppered with dark
blue discs not seen in material from other localities.
United States
A selection of
Ancestral Puebloan (Anasazi) turquoise and orange
argillite inlay pieces from
Chaco Canyon (dated ca. 1020–1140 CE) show the typical colour range and mottling of American turquoise.
Bisbee turquoise commonly has a hard chocolate brown coloured matrix.
The
Southwest United States is a significant source of turquoise;
Arizona,
California (
San Bernardino,
Imperial,
Inyo counties),
Colorado (
Conejos,
El Paso,
Lake,
Saguache counties),
New Mexico (
Eddy,
Grant,
Otero,
Santa Fe counties)
Nevada (
Clark,
Elko,
Esmeralda County,
Eureka,
Lander,
Mineral County and
Nye counties) are (or were) especially rich. The deposits of California and New Mexico were mined by
pre-Columbian Native Americans using stone tools, some local and some from as far away as central
Mexico.
Cerrillos,
New Mexico is thought to be the location of the oldest mines; prior to
the 1920s, the state was the country's largest producer; it is more or
less exhausted today. Only one mine in California, located at Apache
Canyon, operates at a commercial capacity today.
The turquoise occurs as vein or seam fillings, and as compact
nuggets; these are mostly small in size. While quite fine material is
sometimes found—rivalling Iranian material in both colour and
durability—most American turquoise is of a low grade (called "chalk
turquoise"); high iron levels mean greens and yellows predominate, and a
typically friable consistency in the turquoise's untreated state
precludes use in
jewellery .
Arizona is currently the most important producer of turquoise by value.
[5]
Several mines exist in the state, two of them famous for their unique
colour and quality and considered the best in the industry: the Sleeping
Beauty Mine in
Globe, and the
Kingman
Mine that operates alongside a copper mine outside of the city. Other
active mines include the Blue Bird mine, Castle Dome, and Ithaca Peak.
The mines at Morenci, Bisbee, and Turquoise Peak are either inactive or
depleted.
Nevada is the country's other major producer, with more than 120
mines which have yielded significant quantities of turquoise. Unlike
elsewhere in the US, most Nevada mines have been worked primarily for
their gem turquoise and very little has been recovered as a byproduct of
other mining operations. Nevada turquoise is found as nuggets, fracture
fillings and in breccias as the cement filling interstices between
fragments. Because of the geology of the Nevada deposits, a majority of
the material produced is hard and dense, being of sufficient quality
that no treatment or enhancement is required. While nearly every county
in the state has yielded some turquoise, the chief producers are in
Lander and Esmeralda Counties. Most of the turquoise deposits in Nevada
occur along a wide belt of
tectonic activity that coincides with the state's zone of
thrust faulting. It
strikes
about N15°E and extends from the northern part of Elko County,
southward down to the California border southwest of Tonopah. Nevada has
produced a wide diversity of colours and mixes of different matrix
patterns, with turquoise from Nevada coming in various shades of blue,
blue-green, and green. Some of this unusually coloured turquoise may
contain significant zinc and iron, which is the cause of the beautiful
bright green to yellow-green shades. Some of the green to green yellow
shades may actually be
variscite or
faustite,
which are secondary phosphate minerals similar in appearance to
turquoise. A significant portion of the Nevada material is also noted
for its often attractive brown or black limonite veining, producing what
is called "spiderweb matrix". While a number of the Nevada deposits
were first worked by Native Americans, the total Nevada turquoise
production since the 1870s has been estimated at more than 600 tons,
including nearly 400 tons from the Carico Lake mine. In spite of
increased costs, small scale mining operations continue at a number of
turquoise properties in Nevada, including the Godber, Orvil Jack and
Carico Lake Mines in Lander County, the Pilot Mountain Mine in Mineral
County, and several properties in the Royston and Candelaria areas of
Esmerelda County.
[6]
Untreated turquoise, Nevada USA. Rough nuggets from the McGinness Mine,
Austin; Blue and green cabochons showing spiderweb, Bunker Hill Mine,
Royston
In 1912, the first deposit of distinct, single-crystal turquoise was discovered in
Lynch Station,
Campbell County,
Virginia. The crystals, forming a
druse
over the mother rock, are very small; 1 mm (0.04 in) is considered
large. Until the 1980s Virginia was widely thought to be the only source
of distinct crystals; there are now at least 27 other localities.
[7]
In an attempt to recoup profits and meet demand, some American turquoise is treated or
enhanced
to a certain degree. These treatments include innocuous waxing and more
controversial procedures, such as dyeing and impregnation (see
Treatments).
There are however, some American mines which produce materials of high
enough quality that no treatment or alterations are required. Any such
treatments which have been performed should be disclosed to the buyer on
sale of the material.
Other sources
China
has been a minor source of turquoise for 3,000 years or more.
Gem-quality material, in the form of compact nodules, is found in the
fractured, silicified
limestone of
Yunxian and
Zhushan,
Hubei province. Additionally,
Marco Polo reported turquoise found in present-day
Sichuan. Most Chinese material is exported, but a few carvings worked in a manner similar to
jade exist. In
Tibet, gem-quality deposits purportedly exist in the mountains of
Derge and
Nagari-Khorsum in the east and west of the region respectively.
[8]
Other notable localities include:
Afghanistan;
Australia (
Victoria and
Queensland); north
India; northern
Chile (
Chuquicamata);
Cornwall;
Saxony;
Silesia; and
Turkestan.
History of its use
Trade in turquoise crafts, such as this freeform pendant dating from 1000–1040
CE, is believed to have brought the Ancestral Puebloans of the Chaco Canyon great wealth.
Moche turquoise nose ornament.
Larco Museum Collection. Lima-Peru
Backswords, inlaid with turquoise. Russia, 17th century.
Turquoise mosaic mask of
Xiuhtecuhtli, the aztec god of fire.
The pastel shades of turquoise have endeared it to many great cultures of antiquity: it has adorned the rulers of
Ancient Egypt, the
Aztecs (and possibly other Pre-Columbian
Mesoamericans),
Persia,
Mesopotamia, the
Indus Valley, and to some extent in ancient
China since at least the
Shang Dynasty.
[9] Despite being one of the oldest gems, probably first introduced to
Europe (through
Turkey) with other
Silk Road
novelties, turquoise did not become important as an ornamental stone in
the West until the 14th century, following a decline in the
Roman Catholic Church's influence which allowed the use of turquoise in secular jewellery. It was apparently unknown in
India until the
Mughal period, and unknown in
Japan
until the 18th century. A common belief shared by many of these
civilizations held that turquoise possessed certain prophylactic
qualities; it was thought to change colour with the wearer's health and
protect him or her from untoward forces.
The Aztecs inlaid turquoise, together with
gold,
quartz,
malachite,
jet,
jade,
coral, and
shells, into provocative (and presumably ceremonial)
mosaic objects such as
masks (some with a
human skull as their base),
knives, and
shields. Natural
resins,
bitumen and
wax were used to bond the turquoise to the objects' base material; this was usually
wood, but
bone and shell were also used. Like the Aztecs, the
Pueblo,
Navajo and
Apache tribes cherished turquoise for its amuletic use; the latter tribe believe the stone to afford the
archer dead aim. Among these peoples turquoise was used in
mosaic inlay, in sculptural works, and was fashioned into toroidal beads and freeform pendants. The
Ancestral Puebloans (Anasazi) of the
Chaco Canyon
and surrounding region are believed to have prospered greatly from
their production and trading of turquoise objects. The distinctive
silver
jewellery produced by the Navajo and other Southwestern Native American
tribes today is a rather modern development, thought to date from circa
1880 as a result of European influences.
In Persia, turquoise was the
de facto national stone for millennia, extensively used to decorate objects (from
turbans to
bridles),
mosques, and other important buildings both inside and out, such as the Medresseh-I Shah Husein Mosque of
Isfahan. The Persian style and use of turquoise was later brought to
India following the establishment of the Mughal Empire there, its influence seen in high purity
gold jewellery (together with
ruby and
diamond) and in such buildings as the
Taj Mahal. Persian turquoise was often
engraved with devotional words in
Arabic script which was then inlaid with gold.
Cabochons of imported turquoise, along with coral, was (and still is) used extensively in the silver and gold jewellery of
Tibet and
Mongolia,
where a greener hue is said to be preferred. Most of the pieces made
today, with turquoise usually roughly polished into irregular cabochons
set simply in silver, are meant for inexpensive export to Western
markets and are probably not accurate representations of the original
style.
The Egyptian use of turquoise stretches back as far as the
First Dynasty and possibly earlier; however, probably the most well-known pieces incorporating the gem are those recovered from
Tutankhamun's tomb, most notably the
Pharaoh's iconic burial mask which was liberally inlaid with the stone. It also adorned
rings and great sweeping
necklaces called
pectorals. Set in gold, the gem was fashioned into beads, used as inlay, and often carved in a
scarab motif, accompanied by
carnelian,
lapis lazuli, and in later pieces, coloured
glass. Turquoise, associated with the goddess
Hathor,
was so liked by the Ancient Egyptians that it became (arguably) the
first gemstone to be imitated, the fair structure created by an
artificial glazed
ceramic product known as
faience.
The
French conducted
archaeological
excavations of Egypt from the mid-19th century through the early 20th.
These excavations, including that of Tutankhamun's tomb, created great
public interest in the western world, subsequently influencing
jewellery,
architecture, and
art of the time. Turquoise, already favoured for its pastel shades since c. 1810, was a staple of
Egyptian Revival pieces. In contemporary Western use, turquoise is most often encountered cut
en cabochon
in silver rings, bracelets, often in the Native American style, or as
tumbled or roughly hewn beads in chunky necklaces. Lesser material may
be carved into
fetishes, such as those crafted by the
Zuni. While strong sky blues remain superior in value, mottled green and yellowish material is popular with
artisans. In Western culture, turquoise is also the traditional
birthstone for those born in the month of December. The turquoise is also a stone in the Jewish
High Priest's
breastplate, described in
Exodus 28.
Culture
In many cultures of the Old and New Worlds, this gemstone has been
esteemed for thousands of years as a holy stone, a bringer of good
fortune or a talisman. It really does have the right to be called a
'gemstone of the peoples'. The oldest evidence for this claim was found
in
Ancient Egypt, where grave furnishings with turquoise inlay were discovered, dating from approximately 3000 BCE. In the ancient
Persian Empire,
the sky-blue gemstones were earlier worn round the neck or wrist as
protection against unnatural death. If they changed colour, the wearer
was thought to have reason to fear the approach of doom. Meanwhile, it
has been discovered that the turquoise certainly can change colour, but
that this is not necessarily a sign of impending danger. The change can
be caused by the light, or by a chemical reaction brought about by
cosmetics, dust or the acidity of the skin.
Imitations
Some natural blue to blue-green materials, such as this botryoidal
chrysocolla with quartz drusy, are occasionally confused with, or used to imitate turquoise.
The Egyptians were the first to produce an artificial imitation of turquoise, in the glazed earthenware product
faience. Later glass and
enamel were also used, and in modern times more sophisticated ceramics,
porcelain,
plastics, and various assembled, pressed, bonded, and
sintered
products (composed of various copper and aluminium compounds) have been
developed: examples of the latter include "Viennese turquoise", made
from precipitated
aluminium phosphate coloured by
copper oleate; and "neolith", a mixture of
bayerite and
copper phosphate. Most of these products differ markedly from natural turquoise in both physical and chemical properties, but in 1972
Pierre Gilson introduced one fairly close to a true
synthetic
(it does differ in chemical composition owing to a binder used, meaning
it is best described as a simulant rather than a synthetic). Gilson
turquoise is made in both a uniform colour and with black "spiderweb
matrix" veining not unlike the natural Nevada material.
The most common imitation of turquoise encountered today is dyed
howlite and
magnesite,
both white in their natural states, and the former also having natural
(and convincing) black veining similar to that of turquoise. Dyed
chalcedony,
jasper, and
marble
is less common, and much less convincing. Other natural materials
occasionally confused with or used in lieu of turquoise include:
variscite and
faustite;
[5] chrysocolla (especially when impregnating
quartz);
lazulite;
smithsonite;
hemimorphite;
wardite; and a
fossil bone or
tooth called
odontolite or "bone turquoise", coloured blue naturally by the mineral
vivianite.
While rarely encountered today, odontolite was once mined in large
quantities—specifically for its use as a substitute for turquoise—in
southern
France.
These fakes are detected by
gemmologists
using a number of tests, relying primarily on non-destructive, close
examination of surface structure under magnification; a featureless,
pale blue background peppered by flecks or spots of whitish material is
the typical surface appearance of natural turquoise, while manufactured
imitations will appear radically different in both colour (usually a
uniform dark blue) and texture (usually granular or sugary). Glass and
plastic will have a much greater translucency, with bubbles or flow
lines often visible just below the surface. Staining between grain
boundaries may be visible in dyed imitations.
Some destructive tests may, however, be necessary; for example, the application of diluted hydrochloric acid will cause the
carbonates odontolite and magnesite to
effervesce and howlite to turn green, while a heated probe may give rise to the pungent smell so indicative of plastic. Differences in
specific gravity,
refractive index, light absorption (as evident in a material's
absorption spectrum), and other physical and optical properties are also considered as means of separation.
Treatments
An early turquoise mine in the Madan village of Khorasan.
Turquoise is treated to enhance both its colour and durability (i.e., increased
hardness and decreased
porosity).
As is so often the case with any precious stones, full disclosure about
treatment is frequently not given. It is therefore left to
gemologists
to detect these treatments in suspect stones using a variety of testing
methods—some of which are necessarily destructive. For example, the use
of a heated probe applied to an inconspicuous spot will reveal oil,
wax, or plastic treatment with certainty.
Waxing and oiling
Historically, light waxing and oiling were the first treatments used
in ancient times, providing a wetting effect, thereby enhancing the
colour and lustre. This treatment is more or less acceptable by
tradition, especially because treated turquoise is usually of a higher
grade to begin with. Oiled and waxed stones are prone to "sweating"
under even gentle heat or if exposed to too much sun, and they may
develop a white surface film or bloom over time. (With some skill, oil
and wax treatments can be restored.)
Stabilization
Material treated with plastic or water glass is termed "bonded" or
"stabilized" turquoise. This process consists of pressure impregnation
of otherwise unsaleable chalky American material by
epoxy and
plastics (such as
polystyrene) and
water glass (sodium silicate)
to produce a wetting effect and improve durability. Plastic and water
glass treatments are far more permanent and stable than waxing and
oiling, and can be applied to material too chemically or physically
unstable for oil or wax to provide sufficient improvement. Conversely,
stabilization and bonding are rejected by some as too radical an
alteration.
[10]
The epoxy binding technique was first developed in the 1950s and has
been attributed to Colbaugh Processing of Arizona, a company that still
operates today. The majority of American material is now treated in this
manner although it is a costly process requiring many months to
complete. Without such impregnation, most American mining operations
would be unprofitable.
Dyeing
The use of
Prussian blue
and other dyes (often in conjunction with bonding treatments) to
"enhance"—that is, make uniform or completely change—colour is regarded
as fraudulent by some purists,
[10] especially since some dyes may fade or rub off on the wearer. Dyes have also been used to darken the veins of turquoise.
Reconstitution
Perhaps the most extreme of treatments is "reconstitution", wherein
fragments of fine turquoise material, too small to be used individually,
are powdered and then bonded to form a solid mass. Very often the
material sold as "reconstituted" turquoise is
artificial, with little or no natural stone, and may have foreign filler material added to it.
Backing
Since finer turquoise is often found as thin seams, it may be
glued
to a base of stronger foreign material as a means of reinforcement.
These stones are termed "backed," and it is standard practice that all
thinly cut turquoise in the Southwestern United States is backed.
Native indigenous peoples
of this region, because of their considerable use and wearing of
turquoise, have found that backing increases the durability of thinly
cut slabs and cabs of turquoise. They observe that if the stone is not
backed it will often crack. Early backing materials included the casings
of old model T batteries, old phonograph records, and more recently
epoxy steel resins. Backing of turquoise is not widely known outside of
the
Native American
and Southwestern United States jewellery trade. Backing does not
diminish the value of high quality turquoise, and indeed the process is
expected for most thinly cut American commercial gemstones.
[citation needed]
Valuation and care
Slab of turquoise in matrix showing a large variety of different colouration
Hardness and richness of colour are two of the major factors in
determining the value of turquoise; while colour is a matter of
individual taste, generally speaking, the most desirable is a strong sky
to "robin's egg" blue (in reference to the eggs of the
American Robin).
[8]
Whatever the colour, turquoise should not be excessively soft or
chalky; even if treated, such lesser material (to which most turquoise
belongs) is liable to fade or discolour over time and will not hold up
to normal use in jewellery.
The mother rock or
matrix in which turquoise is found can
often be seen as splotches or a network of brown or black veins running
through the stone in a netted pattern; this veining may add value to the
stone if the result is complementary, but such a result is uncommon.
Such material is sometimes described as "spiderweb matrix"; it is most
valued in the
Southwest United States and
Far East, but is not highly appreciated in the
Near East
where unblemished and vein-free material is ideal (regardless of how
complementary the veining may be). Uniformity of colour is desired, and
in finished pieces the quality of workmanship is also a factor; this
includes the quality of the polish and the symmetry of the stone.
Calibrated stones—that is, stones adhering to standard jewellery setting
measurements—may also be more sought after. Like
coral and other opaque gems, turquoise is commonly sold at a price according to its physical size in millimetres rather than weight.
Turquoise is
treated
in many different ways, some more permanent and radical than others.
Controversy exists as to whether some of these treatments should be
acceptable, but one can be more or less forgiven universally: This is
the
light waxing or
oiling
applied to most gem turquoise to improve its colour and lustre; if the
material is of high quality to begin with, very little of the wax or oil
is absorbed and the turquoise therefore does not "rely" on this
impermanent treatment for its beauty. All other factors being equal,
untreated turquoise will always command a higher price. Bonded and
"reconstituted" material is worth considerably less.
Being a
phosphate mineral, turquoise is inherently fragile and sensitive to solvents;
perfume and other
cosmetics
will attack the finish and may alter the colour of turquoise gems, as
will skin oils, as will most commercial jewellery cleaning fluids.
Prolonged exposure to direct sunlight may also discolour or dehydrate
turquoise. Care should therefore be taken when wearing such jewels:
cosmetics, including
sunscreen and
hair spray,
should be applied before putting on turquoise jewellery, and they
should not be worn to a beach or other sun-bathed environment. After
use, turquoise should be gently cleaned with a soft cloth to avoid a
build up of residue, and should be stored in its own container to avoid
scratching by harder gems. Turquoise can also be adversely affected if
stored in an airtight container.
Gallery
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Turquoise tiles on the facade of the Dome of the Rock in Jerusalem.
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Cupula of the famous Tilla Kari Mosque in Samarkand, Uzbekistan.
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The portal of the St. Petersburg mosque.
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The turquoise domes of the Qol-Şärif mosque in Kazan.
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The Madrassa of Ulugh Beg at the Registan Mosque Complex in Samarkand.
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The Abbasid Ivan of the Goharshad mosque in Mashad, Iran.
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The dome and minaret of the Isfahan Royal Mosque in Isfahan, Iran.
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Minaret of the Koutoubia Mosque in Marrakesh, Morocco.
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The mausoleum of the Persian mystic Jalal ad-Din Muhammad Rumi at Konya, Turkey.
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The Rawze-e-Sharif at Mazar-i-Sharif in Afghanistan.
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