Monday, 18 February 2013

Introduction to Topaz Gemstone

Yellow topaz
Silicate of aluminum containing fluorine and hydroxyl In earlier times, the name topaz mainly referred to a gem stone, olivine, extracted on an island then known as Topazos or St. John, and now called Zebirget in the Red Sea It was probably also given to other, yellowish or yeller stones which were indistinguishable from one another without an adequate knowledge of chemistry and mineralogy. The name began to be applied to the mineral and gemstone now known as topaz in the first half of the eighteenth century.

Crystal system


Orthorhombic

Appearance


Often found in short to long prismatic crystals, sometimes with characteristic terminal faces. II often white, semiopaque, milky, or tinged a dirty yellow, but may be transparent, colorless, honey colored, golds brown, brown, or blue; much more rarely, pink or reddish The transparent, colored crystals, which also have gm luster, are widely used as gems.

Physical properties


It has a hardness of 8 and a density of 3.52-3.56 g /cm3. The refractive indices are roughly 1.610, n 1.618 or no 1.630, n1.638. The density se: refractive indices are interrelated and depend on thew-, position of the specimen: topazes richest in hydroxyl have a low density and high refractive indices, where those richest in fluorine have a higher density and low refractive indices. The stone has easy perfect basal cleavage.

Genesis


Topaz crystal Topaz is characteristic of pegmatite and pneumatolytic deposits and is therefore found in dykes m: contact aureoles around granitic intrusions. It is also found in alluvial deposits, but is, perhaps, the most vulnerable' the harder gemstones to attack by the elements, at least in tropical or equatorial regions.

Occurrence


The mineral first classified scientifically et topaz came from Saxony The topazes of Brazil are famous, some being of gigantic proportions. Topazes as also found in Mexico, the United States, Sri Lanka. JO) the Soviet Union (both in Siberia and in the Urals), Nigeria and Zaire to mention just the main sources

Topaz


True topaz or yellow topaz is the most typical variety, no adjectives are needed to describe its color, at different shades are sometimes referred to as 'go topaz" or "sherry topaz.-

Appearance


The color can range from golden to toe yellow or can be golden brown or honey with a pink oral dish tinge. The crystals are usually cut into oval gems pear and other mainly elongated shapes are also produced, usually with a crown and pavilion consisting of many small lozenge-shaped facets, which bring luster of the stone. The longer stones often look darkish at the ends. Easy basal cleavage makes these gems rather brittle, so they should be treated with care and protected from the type of sharp blows to which ring stones are susceptible. Medium-large stones are relatively common aria even very large ones are not rare.

Distinctive features


Yellow topazA great deal of citrine quartz, which looks fairly similar, is sold under the name of topaz or topaz citrine, creating some confusion on the market. The color of topaz is, however, generally much warmer and more likely to have an orange or pinkish stone; the stone will also have a much greater luster. In any event, a quick check of the density, perhaps using one of the heavy liquids, woul1 immediately distinguish between the two, and measurement of the refractive indices would remove all trace e doubt.

Occurrence


Topaz comes mainly from Brazil, and in smaller quantities, from the Soviet Union, Japan, Sri Lanka, Burma and the United States. It is occasionally found in Germany.

Value


Well colored, medium-large specimens of true topaz are quite valuable, but perhaps less so today, than is the past. Roughly on a par with secondary gemstones, such as the better tourmalines, it has probably suffered from the ready availability of citrine quartz, an intend stone, which by usurping the name, has made topaz seem more abundant than it really is.

Simulants and synthetics


The main problem is hit practice of passing citrine quartz off as topaz. Synthetic corundum of a color similar to topaz has also been produced by way of imitation, whereas topaz itself has often been synthesized on a limited scale for scientific purpose and is not found on the market.

Pink topaz


Violet pink topazAs already mentioned, true or yellow topaz may be Pinkish orange or yellow with a pink tinge. There is in fact a whole range of color gradations from yellow to pink, and it is heard to establish a dividing line between the two varieties.

Appearance


In some cases the color is pink with a distinctive yellowish or orange shade, but it is more alkyl definite lights to medium pink, tending to red or violet a deeper colored stones. The color is not always evenly distributed and can show slight crystallographic zoning stones usually have few inclusions and are strongly tears parent and lustrous.

The most common cut is the oval or pear shape, but many other old or antique faceted cuts are seen, as is the step cut. While it has always been comparatively rare pink topaz was much appreciated in antique jewelry and store weighing up to 10 carats are often found.

Distinctive features


At first sight, there is not a lot difference between pink topaz, kunzite, morganite, arid some pink tourmalines. But a density test with a heavy IV such as methylene iodide, in which topaz sinks but in others float will distinguish topaz from the others. It is harder to tell pink topaz apart from pink spinel and corundum, the former having about the same density al topaz, and the latter having a higher density. In case of confusion with these stones, other properties, such as the refractive indices, need to be examined.

Occurrence


Pink topaz comes mainly from Brazil, but has also been mined recently in the Ural Mountains of the Soviet Union. In both places, intensely colored reddish or purplish specimens have very occasionally been found.

Value


Pink topaz When the color is fairly intense, it is one of the most valuable of the second level of gemstones (e.g. aqua-marine). Specimens that are too pale have a low value. Like yellow topaz, it was perhaps more highly prized in the past than today.

Simulants and synthetics


At one time glass imitations were occasionally produced. In antique jewelry, very pale stones were sometimes given a closed setting with a painted base to heighten their color. The pink color of many topazes is due to heat treatment of pinkish-yellow stones from Brazil. This method goes back at least several centuries, so even antique stones may have been colored in this way. This procedure, however, has always been regarded as admissible in the gem trade, so the question of whether the color of pink topaz is natural or due to heat treatment does not arise.

Blue topaz


This is the variety of topaz most readily available on the market today.

Appearance


It has a definite, uniform sky-blue color, usually without any overtones. Often pale, it can be bright or very rarely an intense blue. It sometimes has a slight gray or even greenish tinge, giving it a lifeless appearance. Gemstones of several carats or even several tens of carats in weight are relatively common. Furthermore, they are usually wholly or almost free of inclusions. This is often the case where large amounts of material of no great value are available: the less clear pieces are discarded. The most common cut is the oval, with the crown and pavilion consisting of very many lozenge-shaped facets, but all the mixed cuts, plus the step cut, are used. As With all light colored gemstones, the value of blue topaz increases with intensity of color, provided this is attractive and not somber. Like other types of topaz, it cleaves readily and this can affect its durability.

Distinctive features


Blue topaz There is, at first sight, some resemblance to aquamarine; but close observation will distill-quash the two, as aquamarine always displays a very attractive pleochroism from blue to greenish blue or even bluish green. Topaz is usually a more definite blue, it anything with a grayish tone, which certainly distinguishes from aquamarine. Meastirement of the density atone is not enough to distinguish topaz from synthetic blue spinel which can be very similar in color. Before measuring other physical properties, such as the refractive indices, the stone can be examined under a lens for signs of birefringence. Although taint a doubling of the facet edges will be visible in topaz. If this is present, one can immediately rule out the possibility of its being synthetic spinet or glass, both of which are singly refractive.

Occurrence


Blue topaz is found in various parts of Brazil, Mexico, and the United States. It is mined in Burma (in the Mogok region famous for rubies) and the Soviet Union (chiefly in the Urals and the Kamchatka peninsula). It is also found in Namibia and Nigeria.

Value


Quite low several times less than that of aquamarine. The ready availability of blue topaz on the market, even in pieces of considerable size, is probably responsible for this.

Simulants and synthetics  


Colorless topaz
Because blue topaz is a relatively minor gemstone compared with aquamarine, it is the latter that is imitated by glass or synthetic blue spinet AI-though blue topaz has not been manufactured synthetically on a commercial scale, a completely natural-looking blue coloration has been produced during recent years in color-less topaz by means of irradiation. This practice, regarded as legitimate in the trade, unless performed in such a way as to cause appreciable residual radiation (fortunately, very uncommon), is becoming increasingly widespread and is one of the reasons for the present abundance of blue topaz.

Colorless topaz


As a mineral, this is far and away the most common variety of transparent topaz, although it is of limited importance as a gemstone. All colorless gemstones compare most unfavorably with diamond, their lower refractive indices and lesser dispersion making them far less attractive. Tops have the advantage over the others of being found in large stones and great quantities, and of having good hardness and luster. Therefore it is of some interest to hobbyists.

Appearance


Gemstones are generally free, or alimonies of inclusions because they can be culled from the large quantities available; but they may show signs of extensive internal cleavage. In large stones (of a few centimeters) Its mineral's weak birefringence can be detected with the sale of a lens, the facet edges appearing double when seen through a flat facet of the stone. The stones easily acquire good luster and are only disappointing on the rare occasions when they are given the brilliant cut, prompting comparison with diamonds, which have a very different luster and "fire."

Distinctive features


Ring with yellow topaz. Colorless topaz differs little from the colorless varieties of other minor gems, which, with the exception of quartz, are all much rarer. Incipient cleavage, where present, may be a distinguishing feature. If the edges appear double, denoting birefringence, this candle distinguishes it from synthetic colorless spinet, which has a semidensity: but it cannot differentiate it from other min°, (-QV gemstones such as colorless beryl, tourmaline, and confaldum. To distinguish it with any certainty from these, theft refractive indices must be determined.

Occurrence  


It is found in various parts of Brazil, the Soviet Union, the United States, Germany (Saxony), mg Japan. Africa, too, has a plentiful supply of colorless topaz in the tin-mining areas of both Nigeria and Zaire. It is* found in Namibia.

Value


One of the lowest for transparent gemstones even, though it is greatly appreciated by amateur cutters as a raw material. Apparently, it is being used increasingly for the production of blue topaz by means of irradiation.

Simulants and synthetics


It is neither imitated nor produced synthetically.

Writer – Curzio Cipriani and Alessandro Borelli
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2 comments:

  1. Although the topaz of pure quality is simply colorless, but it also occurs in varied colors and the blue one is the most popular. The popularity that this stone has acquired can be understood well by the sheer fact that it can be found everywhere in the market, and there is no dearth of buyers for it.

    For More Information about Swiss Blue Topaz Visit:
    http://www.swissbluetopaz.com/

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