TIGER’S EYE[GEM]
Listing description
Tiger's eye (also called Tigers eye or Tiger
eye) is a chatoyant gemstone
that is usually a metamorphic rock that is a golden to red-brown color, with a
silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite
(blue asbestos).
Detailed description
Tiger's
eye (also called Tigers
eye or Tiger eye) is a chatoyant gemstone that is usually a metamorphic rock that is a golden to red-brown color,
with a silky luster. A member of the quartz group, it is a classic example of pseudomorphous replacement by silica of fibrous crocidolite (blue asbestos). An incompletely
silicified blue variant is called Hawk's eye.
Cut, treatment, and imitation
The gems are
usually cut en cabochon in order to best display their chatoyancy. Red stones are brought about through
gentle heat treatment. Honey-colored stones have been used to imitate the much
higher valued cat's eye chrysoberyl (cymophane), but the overall effect
is unconvincing. Artificial fiberoptic glass is a common imitation of
tiger's eye, and is produced in a wide range of colors. Tiger's Eye mostly
comes from South
Africa and East Asia.
Tiger iron
Tiger
iron is an altered rock composed chiefly of tiger's eye, red jasper, and black hematite. The undulating, contrasting bands of
color and luster make for an attractive motif, and it is mainly used for
jewelry-making and ornamentation. Tiger iron is a popular ornamental material
used in a variety of applications, from beads to knife hilts. Along with tiger's eye it is mined primarily
in South
Africa and Western Australia. Tiger's eye is primarily composed of
silicon
dioxide (SiO2)
and is colored mainly by iron oxide. The specific gravity ranges from 2.64 -2.71.[1] It is formed by the alteration of
crocidolite.
Quartz is the second most abundant mineral
in the Earth's
continental crust, after feldspar.
It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra,
with each oxygen being shared between two tetrahedra, giving an overall formula
SiO2.There are many different varieties of quartz, several of which are semi-precious gemstones. Especially in Europe and the Middle East, varieties of quartz have been since antiquity the most commonly used minerals in the making of jewelry and hardstone carvings.
The word "quartz" is derived from the German word "quarz", which was imported from Middle High German, "twarc", which originated in Slavic (cf. Czech tvrdy ("hard"), Polish twardy ("hard"), Russian твёрдый ("hard")), from Old Bulgarian (Church Slavonic) тврьдъ ("firm"), from Proto-Slavic *tvьrdъ.[6]
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Crystal habit
At surface temperatures and pressures, quartz is the most stable form of silicon dioxide. Quartz will remain stable up to 573 °C at 1 kilobar of pressure. As the pressure increases the temperature at which quartz will lose stability also increases.
Above 1300 °C and at a pressure of approximately 35 kilobars, only β-quartz is stable. The latter is not the same as normal quartz (or α-quartz), low quartz or just quartz. β-quartz has higher symmetry, is less dense and has a slightly lower specific gravity. The conversion, from one solid substance to another solid substance, of quartz to β-quartz is quick, reversible and accompanied with a slight energy absorption. The conversion is so easily accomplished that when a crystal of quartz is heated to β-quartz, cooled back down, heated again to β-quartz, etc., the quartz will be the same as when it started.
The reason that the conversion is so easily accomplished is that the difference between quartz and β-quartz is relatively slight. The bonds between the oxygen and silicon atoms are "kinked" or bent in quartz and are not so "kinked" in β-quartz. At the higher temperatures the atoms move away from each other just enough to allow the bonds to unkink or straighten and produce the higher symmetry. As the temperature is lowered, the atoms close in on each other and the bonds must kink in order to be stable and this lowers the symmetry back down again.
Although all quartz at temperatures lower than 573 °C is low quartz, there are a few examples of crystals that obviously started out as β-quartz. Sometimes these are labeled as β-quartz but are actually examples of pseudomorphic or "falsely shaped" crystals more correctly labeled 'quartz after β-quartz'. These crystals are of higher symmetry than low quartz although low quartz can form similar crystals to them. They are composed of hexagonal dipyramids which are a pair of opposing six sided pyramids and the crystals lack prism faces. Quartz's typical termination is composed of two sets of three rhombic faces that can look like a six sided pyramid.
(Microscopic)
crystal structure
α-quartz
crystallizes in the trigonal crystal system, space group P3121
and P3221 respectively. β-quartz belongs to the hexagonal
system, space group P6221 and P6421,
respectively.[7]
These spacegroups are truly chiral (they each belong to the 11 enantiomorphous
pairs). Both α-quartz and β-quartz are examples of chiral crystal structures
composed of achiral building blocks (SiO4 tetrahedra in the present
case). The transformation between α- and β-quartz only involves a comparatively
minor rotation of the tetrahedra with respect to one another, without change in
the way they are linked.
Varieties (according to color)
Pure
quartz, traditionally called rock crystal (sometimes called clear
quartz), is colorless and transparent (clear) or translucent,
and has often been used for hardstone
carvings, such as the Lothair
Crystal. Common colored varieties include citrine, rose quartz, amethyst,
smoky quartz, milky quartz, and others. Quartz goes by an array of different
names. The most important distinction between types of quartz is that of macrocrystalline
(individual crystals visible to the unaided eye) and the microcrystalline
or cryptocrystalline varieties (aggregates of crystals
visible only under high magnification). The cryptocrystalline varieties are
either translucent or mostly opaque, while the transparent varieties tend to be
macrocrystalline. Chalcedony is a cryptocrystalline form of
silica consisting of fine intergrowths of both quartz, and its monoclinic
polymorph moganite.[8]
Other opaque gemstone varieties of quartz, or mixed rocks including quartz,
often including contrasting bands or patterns of color, are agate,
sard,
onyx,
carnelian,
heliotrope, and jasper.
Occurrence
Quartz is an
essential constituent of granite and other felsic igneous rocks. It is very common in sedimentary rocks such as sandstone and shale and is also present in variable amounts as an
accessory mineral in most carbonate rocks. It is also a common constituent of schist, gneiss, quartzite and other metamorphic rocks. Because of its resistance to weathering it is very common in stream sediments
and in residual soils. Quartz, therefore, occupies the
lowest potential to weather in the Goldich
dissolution series.
Quartz occurs in hydrothermal veins as gangue along with ore minerals. Large crystals of quartz are found
in pegmatites. Well-formed crystals may reach
several meters in length and weigh hundreds of kilograms.
Naturally
occurring quartz crystals of extremely high purity, necessary for the crucibles
and other equipment used for growing silicon wafers in the semiconductor industry, are expensive and rare. A
major mining location for high purity quartz is the Spruce Pine Gem Mine in Spruce
Pine, North Carolina,
United
States.[13]
Related silica minerals
Tridymite and cristobalite are high-temperature polymorphs of SiO2 that occur in high-silica volcanic rocks. Coesite is a denser polymorph of quartz found
in some meteorite impact sites and in metamorphic rocks formed at pressures
greater than those typical of the Earth's crust. Stishovite is a yet denser and higher-pressure
polymorph of quartz found in some meteorite impact sites. Lechatelierite is an amorphous silica glass SiO2 which is formed by lightning strikes in quartz sand.
History
Quartz is the
most common material identified as the mystical substance maban in Australian Aboriginal mythology. It is found regularly in passage
tomb cemeteries in Europe in a burial context, such as Newgrange or Carrowmore in the Republic
of Ireland.
The Irish word for quartz is grian cloch,
which means 'stone of the sun'. Quartz was also used in Prehistoric
Ireland, as well as many
other countries, for stone tools; both vein quartz and rock crystal
were knapped as part of the lithic technology of the prehistoric peoples.[16]
While jade has been since earliest times the most prized
semi-precious stone for carving in East Asia and Pre-Columbian America, in Europe and the Middle
East the different varieties of quartz were the most commonly used for the
various types of jewelry and hardstone carving, including engraved gems and cameo gems, rock crystal vases, and extravagant vessels. The
tradition continued to produce objects that were very highly valued until the
mid-19th century, when it largely fell from fashion except in jewelry. Cameo
technique exploits the bands of color in onyx and other varieties.
Roman naturalist Pliny the Elder believed quartz to be water ice, permanently frozen after great lengths of
time. (The word "crystal" comes from the Greek word κρύσταλλος,
"ice".) He supported this idea by saying that quartz is found near
glaciers in the Alps, but not on volcanic mountains, and that large quartz
crystals were fashioned into spheres to cool the hands. He also knew of the
ability of quartz to split light into a spectrum. This idea persisted until at least
the 17th century.
PRICE
$66/KG OR $30/IB
For more information:
mobile: +2348039721941
contact person: emeaba uche
e-mail: emeabau@yahoo.com
website: www.franchiseminerals.com
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