Rare natural Australia Fire SOLID Matrix BOULDER Opal Gem Cabachon Estate Piece

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Rare natural Australia Fire SOLID Matrix BOULDER Opal Gem Cabachon Estate Piece:
$15.00

This specimen weighs weighs 0.65 carats, which is 0.12 grams, and measures 7 mm by 5 mm by 3 mm.I offer a shipping discount for customers who combine their payments for multiple purchases into one payment!
The discount is regular shipping price for the first item and just 50 cents for each additional item!
Please be sure to request a combined invoice before you make your payment. Thank you.Hi there, I am selling this really nice Boulder Opal Mineral Specimen Cabochon from Australia . It is really beautiful. It is a collectionpiece of mine that I have had.
Times are tough and I amtrying to raise money, and I thought I would try selling off somethings from my old collection.
I hope it finds a good home out there,and I am sure they will.
This piece is really nice. I purchased it along with some other hand made cabochons from an estate of a really well known lapidary artist.
All the cabs there were fabulous and hand designed. This opal is from Australia, and has TONS OF FIRE!
It is beyond gorgeous and you will love it to death when you get it!
If youhave any questions, do not hesitate to ask me. Have fun offerding, and know that I will ship this out the same day asthe payment clears.
Thanks so much for visiting my sale andhave a great day:>)The following is information about this from wikipedia:OpalFrom Wikipedia, the free encyclopediaJump to: navigation, searchFor other uses, see Opal (disambiguation).

Opal is a mineraloid gel which isdeposited at a relatively low temperature and may occur in the fissuresof almost any kind of rock, being most commonly found with limonite,sandstone,rhyolite,marl and basalt.The word opal comes from the Latin opalus,by Greek ὀπάλλιος opallios.

The water content is usually between three and ten percent, but canbe as high as twenty percent. Opal ranges from clear through white,gray, red, orange, yellow, green, blue, magenta, rose, pink, slate,olive, brown, and black. Of these hues, the reds against black are themost rare, whereas white and greens are the most common. These colorvariations are a function of growth size into the red and infraredwavelengths. Opal is Australia\'s national gemstone.

Contents

1 Precious opal
2 Common opal
3 Other varieties of opal
4 Sources of opal
5 Synthetic opal
6 Local atomic structureof opals
- 6.1 Microcrystalline opal
- 6.2 Non-crystalline opal
7 Historicalsuperstitions
8 Famous opals
9 See also
10 References
11 External links

Precious opalOpals can express every color in the visible spectrum.Precious opal consists of spheres of silica of fairly regular size,packed into close-packed planes which are stacked together withcharacteristic dimensions of several hundred nm.

Precious opal shows a variable interplay of internal colors and eventhough it is a mineraloid, it does have an internal structure.At micro scales precious opal is composed of silica spheres some 150 to300 nmin diameter in a hexagonal or cubic close-packed lattice. These ordered silica spheres produce theinternal colors by causing the interference and diffractionof light passing through the microstructure of the opal.[4]It is the regularity of the sizes and the packing of these spheres thatdetermines the quality of precious opal. Where the distance between theregularly packed planes of spheres is approximately half the wavelengthof a component of visible light, the lightof that wavelength may be subject to diffractionfrom the grating created by the stacked planes.The spacing between the planes and the orientation of planes withrespect to the incident light determines the colors observed. Theprocess can be described by Bragg\'s Law of diffraction.

Visible light of diffracted wavelengths cannot pass through largethicknesses of the opal. This is the basis of the optical band gapin a photonic crystal, of which opal is the bestknown natural example. In addition, microfractures may be filled withsecondary silica and form thin lamellae inside the opal duringsolidification. The term opalescenceis commonly and erroneously used to describe this unique and beautifulphenomenon, which is correctly termed playof color. Contrarily, opalescence is correctly appliedto the milky, turoffer appearance of common or potch opal.Potch does not show a play of color.

The veins of opal displaying the play of color are often quite thin,and this has given rise to unusual methods of preparing the stone as agem. An opal doublet is a thin layer of opal,backed by a swart mineral such as ironstone,basalt,or obsidian.The darker backing emphasizes the play of color, and results in a moreattractive display than a lighter potch.

Combined with modern techniques of polishing, doublet opal producessimilar effect of black or boulder opals at a mere fraction of theprice. Doublet opal also has the added benefit of having genuine opal asthe top visible and touchable layer, unlike triplet opals.

The triplet-cut opal backs the colored material with a dark backing,and then has a domed cap of clear quartz orplastic on top, which takes a high polish and acts as a protective layerfor the relatively fragile opal. The top layer also acts as amagnifier, to emphasize the play of color of the opal beneath, which isoften of lower quality. Triplet opals therefore have a more artificialappearance, and are not classed as precious opal.

Common opal

Besides the gemstone varieties that show a play of color, thereare other kinds of common opal such as the milk opal,milky bluish to greenish (which can sometimes be of gemstone quality), resin opalwhich is honey-yellow with a resinous luster, wood opal which is causedby the replacement of the organic material in wood withopal,[5]menilitewhich is brown or grey, hyalite is a colorless glass-clear opal sometimescalled Muller\'s Glass, geyserite, also called siliceous sinter, deposited around hot springs or geysersand diatomite or diatomaceous earth, the accumulations of diatomshells or tests.

Other varieties of opal

Fire opals are transparent to translucent opals with warm body colorsyellow, orange, orange-yellow or red and they do not usually show anyplay-of-color, although occasionally a stone will exhibit bright greenflashes. The most famous source of fire opals is the state of Querétaroin Mexico and these opals are commonly called Mexican fire opals.

Peruvian opal (also called blue opal) is a semi-opaque to opaqueblue-green stone found in Peru which is often cut to include the matrixin the more opaque stones. It does not display pleochroism.

Boulder opal carving of a walrus, showing flashes of color from theexposed opal. The carving is 9 cm (3.5 inches) long.Sources of opalPolished opal from Yowah, Queensland, Australia

Australia produces around 97% of the world\'s opal. 90% is called‘light opal’ or white and crystal opal. White makes up 60% of the opalproductions but cannot be found in all of the opal fields. Crystal opalor pure hydrated silica makes up 30% of the opal produced, 8% is blackand only 2% is boulder opal.[citation needed]

The town of Coober Pedy in South Australia is a major source of opal. Andamooka inSouth Australia is also a major producer of matrix opal, crystal opal,and black opal. Another Australian town, Lightning Ridge in New South Wales, is the main source of black opal, opalcontaining a predominantly dark background (dark-gray to blue-blackdisplaying the play of color). Boulder opal consists of concretions andfracture fillings in a dark siliceous ironstonematrix. It is found sporadically in western Queensland, from Kynuna inthe north, to Yowah and Koroit in the south.[6]

Multi-colored rough opal specimen from Virgin Valley, Nevada, USA

The Virgin Valley opal fields of Humboldt County in northern Nevadaproduce a wide variety of precious black, crystal, white, fire, andlemon opal. The black fire opal is the official gemstone of Nevada. Mostof the precious opal is partial wood replacement. Miocene age opalisedteeth, bones, fish, and a snake head have been found. Some of the opalhas high water content and may desiccate and crack when dried. Thelargest black opal in the Smithsonian Institution comes fromthe Royal Peacock opal mine in the Virgin Valley.[citation needed]

Another source of white base opal or creamy opal in the UnitedStates is Spencer, Idaho. Spencer has an open pit minethat you can visit for a fee, about 4 times a year. One business inSpencer also brings material down from the mine site to their store, sothat would be opal miners can dig for their own opal, again for anominal fee. A high percentage of the opal found there occurs in thinlayers. As a result, most of the production goes into the making ofdoublets and triplets.

Other significant deposits of precious opal around the world can befound in the Czech Republic, Slovakia, Hungary, Turkey, Indonesia,Brazil (Pedro II a city in the state of Piauí), Honduras, Guatemala,Nicaragua and Ethiopia.

In late 2008, NASA announced that it had discovered opal deposits on Mars.[7]

Synthetic opal

As well as occurring naturally, opals of all varieties have beensynthesized experimentally and commercially. The discovery of theordered sphere structure of precious opal led to its synthesis by PierreGilson in 1974.[4]The resulting material is distinguishable from natural opal by itsregularity; under magnification, the patches of color are seen to bearranged in a \"lizard skin\" or \"chicken wire\" pattern. Synthetics arefurther distinguished from naturals by the former\'s lack of fluorescenceunder UV light. Synthetics are also generally lower indensity and are often highly porous.

Two notable producers of synthetic opal are the companies Kyoceraand Inamori of Japan.Most so-called synthetics, however, are more correctly termed\"imitation opal\", as they contain substances not found in natural opal(e.g., plastic stabilizers). The imitation opals seen in vintage jewelryare often foiled glass, glass-based \"Slocumstone\", or later plastic materials.

Local atomicstructure of opals

The lattice of spheres of opal that cause the interference with lightare several hundred times larger than the fundamental structure ofcrystalline silica. As a mineraloid,there is no unit cell that describes the structure ofopal. Nevertheless, opals can be roughly divided into those that show nosigns of crystalline order (amorphous opal) and those that show signs of thebeginning of crystalline order, commonly termed cryptocrystalline or microcrystallineopal.[8]Dehydration experiments and infrared spectroscopy have shown thatmost of the H2O in the formula of SiO2·nH2Oof opals is present in the familiar form of clusters of molecularwater. Isolated water molecules, and silanols,structures such as Si-O-H, generally form a lesser proportion of thetotal and can reside near the surface or in defects inside the opal.

The structure of low-pressure polymorphs of anhydrous silica consist of frameworks of fully-cornerbonded tetrahedra of SiO4. The higher temperature polymorphsof silica cristobalite and tridymiteare frequently the first to crystallize from amorphous anhydroussilica, and the local structures of microcrystalline opals also appearto be closer to that of cristobaliteand tridymitethan to quartz. The structures of tridymite and cristobalite areclosely related and can be described as hexagonal and cubic close-packed layers. It is therefore possible tohave intermediate structures in which the layers are not regularlystacked.

The crystal structure of crystalline α-cristobalite. Locally, thestructures of some opals, opal-C, are similar to this. Microcrystalline opal

Opal-CT has been interpreted as consisting of clusters of stacking ofcristobalite and tridymite over very short length scales. The spheresof opal in opal-CT are themselves made up of tiny microcrystallineblades of cristobalite and tridymite. Opal-CT has occasionally beenfurther subdivided in the literature. Water content may be as high as 10wt%. Lussatite is a synonym. Opal-C, also called Lussatine, isinterpreted as consisting of localized order of α-cristobalitewith a lot of stacking disorder. Typical water content is about 1.5wt%.

Non-crystalline opal

Two broad categories of non-crystalline opals, sometimes justreferred to as \"opal-A\", have been proposed. The first of these isopal-AG consisting of aggregated spheres of silica, with water fillingthe space in between. Precious opal and potch opal are generallyvarieties of this, the difference being in the regularity of the sizesof the spheres and their packing. The second \"opal-A\" is opal-AN orwater-containing amorphous silica-glass. Hyaliteis another name for this.

Non-crystalline silica in siliceous sediments is reported togradually transform to opal-CT and then opal-C as a result of diagenesis,due to the increasing overburden pressure in sedimentary rocks, as some of the stackingdisorder is removed.[9]

Historicalsuperstitions

In the Middle Ages, opal was considered a stone that could providegreat luck because it was believed to possess all the virtues of eachgemstone whose color was represented in the color spectrum of the opal.[10]It was also said to confer the power of invisibility if wrapped in afresh bayleaf and held in the hand.[10][11]Following the publication of Sir WalterScott\'s Anne of Geierstein in 1829, however, opal acquired aless auspicious reputation. In Scott\'s novel, the Baroness of Arnheimwears an opal talisman with supernatural powers. When a drop of holywater falls on the talisman, the opal turns into a colorless stoneand the Baroness dies soon thereafter. Due to the popularity of Scott\'snovel, people began to associate opals with bad luck and death.[10]Even as recently as the beginning of the 20th century, it was believedthat when a Russian saw an opal among other goods offered for sale, heor she should not buy anything more since the opal was believed toembody the evil eye.[10]

Opal is considered the birthstone for people born in October or underthe sign of Libraand the star stone for people born under Scorpio.

Famous opals

The Andamooka Opal, presented to Queen Elizabeth II, also known asthe Queen\'s Opal
\"The Burning of Troy\", an opal presented to Joséphine de Beauharnais by Napoleon I of France[12]
The Flame Queen Opal
The Halley\'s Comet Opal, the world\'s largestuncut black opal
The Roebling Opal, Smithsonian Institution[13]