ZOISITE Aravindhanmani, group 26. Scientific adviser is Svetlana Kozub.
Zoisite owes much of its popularity to a beautiful blue variety that was first discovered in 1967. This new discovery in Tanzania brought forth a previously unknown color and habit for this mineral. The variety was unofficially named Tanzanite after the county it was found in, and it became an ever-popular gemstone sensation shortly after its discovery. The color of Tanzanite is rarely natural; it is almost heat treated from grayish or brownish hued stones. The heat treatment process removes unwanted color tints and strengthens the desirable blue.
Zoisite occurs in many other colors, and another well-known form is the pink, manganese-rich variety called Thulite. Another interesting variety is the deep green massive form associated with contrasting red Ruby. Zoisite was named in 1805 after Austrian scientist and naturalist Baron Sigmund Zois von Edelstein (1747–1819), who had a notable mineral collection and identified Zoisite as being a unique mineral species. .
Ca2Al3(SiO4)3(OH) Composition Basic calcium aluminum silicate
Color Gray, beige, yellow, brown, green, blue, purple, pink, red. Transparent forms are strongly pleochroic. Streak White.
The more common forms of Zoisite are not of any significant interest, although transparent crystals, especially those rare forms from Pakistan, are highly valued among mineral collectors. The variety Tanzanite has become an extremely popular mineral and gemstone, and is heavily marketed by the jewelry industry. Fine Tanzanite gemstones can be extremely costly and cherished. The pink variety, Thulite, is used as a minor gemstone, and is most often cut as cabochons. The green variety associated with Ruby is also used as a minor gemstone.
VARAITES:
Ruby Zoisite – Mixture of opaque red Ruby in a green Zoisite matrix from Tanzania. Ruby Zoisite has pretty contrast and is used as a minor gemstone.
Tanzanite – Blue to purplish-blue variety of Zoisite found in the Merelani Hills in the Arusha region of Tanzania. Tanzanite is used as an important gemstone and has become enormously popular.
Thulite – Pink, manganese-rich variety of the Zoisite. Originally found in Norway, Thulite is named after the mythical region of Thule, which many identify as Norway. See the gemstone Thulite for additional information, and see also Clinothulite.
TOPAZ Mohamed Asausai Divan Muksheen, group 26. Scientific adviser
is Svetlana Kozub
It is a fluorine aluminium silicate and comes in yellow, yellow-brown, honey-yellow, flax, brown, green, blue, light blue, red and pink ... and sometimes it has no colour at all.
The colour in which the topaz is most commonly found is yellow, and that is the colour in which it occurs in one of the major German gemstone rocks, the Schneckenstein (a topaz-bearing rock said to resemble a snail) in Saxony. In the 18th century, it was mined there during a period of over 60 years. However, most of the crystals were hardly a centimetre in diameter. You had to go to Siberia or Brazil to find crystals as large as your fist. Having said that, anyone who is interested can convince himself of the beauty of cut specimens in the topaz set in Dresden's Grünes Gewölbe (Green Vault). The enormous and magnificent topaz from the Portuguese crown, the Braganza, was for a long time thought to be a diamond. It weighs 1680 ct. In mysticism, the topaz is attributed with a cooling, styptic and appetising effect. It is said to dispel sadness, anger and nocturnal fears, to warn its wearer of poisons and protect him or her from sudden death. It is reputed to make men handsome and intelligent and sterile women fertile and happy. However, it is probably better not to rely too much on its magical powers, since it was also claimed that you could immerse your hand in boiling water after a topaz had been thrown into it and retract it again unharmed! It is the stone of the month November.
In the Empire style, the topaz was still widespread, but then the more reasonably priced citrine took over from it and even usurped its name – gold topaz. Since then, the topaz has been a rather exotic figure in the jewellery trade, and has been given the additional predicate 'pure' to make it clear that the topaz, not the quartz topaz, is meant. And it is still waiting for its well deserved comeback to this day.
The topaz has been known for at least 2000 years and is one of the gemstones which form the foundations of the twelve gates to the Holy City of the New Jerusalem. These so-called apocalyptic stones are intended to serve in protection against enemies and as a symbol of beauty and splendour. It cannot be proved conclusively whether the name of the topaz comes from the Sanskrit or the Greek, though the Greek name 'topazos' means 'green gemstone'. The Romans dedicated the topaz to Jupiter.
GOETHITE
The formation of goethite is marked from the oxidation state change of Fe2+ to Fe3+, which allows for goethite to exist at surface conditions. Because of this oxidation state change, goethite is commonly seen as a pseudomorph.
Goethite is found all over the planet, usually in the form of concretions, stalactitic formations, oolites (a form consisting of tiny round grains cemented together), reniform (kidney shapes) or botryoidal (globular, like bunches of grapes) accumulations. It is also a very common pseudomorph.
It is frequently encountered in the swampy areas at the head of spring waters ('bog iron'), on cave floors, and on the bottom of lakes and small creeks. The boxworks or gossan resulting from the oxidation of sulfide ore deposits is formed of goethite along with other iron oxides and quartz.
Significant deposits of goethite are found in England, Australia, Cuba, and Michigan, Minnesota, Missouri, Colorado, Alabama, Georgia, Virginia, and Tennessee in the United States.
Deposits significant in location, if not in abundance, have been found in Gusev by NASA's Spirit rover, providing strong evidence for the presence of liquid water on the planet Mars in an earlier stage of its evolution.
Its main modern use is as an iron ore, being referred to as brown iron ore. It does have some use as a clay earth pigment. Iron rich lateritic soils developed over serpentinite rocks in tropical climates are mined for their iron content as well as other metals. Fine goethite specimens are rare and therefore are valued collectibles. Banded or iridescent varieties are cut and polished into cabochons for jewelry making. Color: Yellowish to reddish to dark brown or black. Crystal habit: radial acicular, massive, as encrustation, as pseudomorph; may be banded or iridescent. Crystal System: Orthorhombic 2/m2/m2/m. Fracture: Uneven to Splentery.
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