Opal
An opal bracelet. The stone size is 18 by 15 mm (0. 7 by 0. 6 inch).
General
Category	Mineraloid
Chemical formula	Hydrated silica. A mineraloid is a Mineral -like substance that does not demonstrate Crystallinity. A chemical formula is a way of expressing information about the Atoms that constitute a particular Chemical compound, and how the relationship between those atoms changes Hydrate is a term used in Inorganic chemistry and Organic chemistry to indicate that a substance contains Water. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide SiO2·nH2O
Identification
Color	White, black, red, orange, most of the full spectrum, colorless, iridescent. Iridescence is an Optical phenomenon in which Hue changes with the angle from which a surface is viewed Very infrequently of a singular color
Crystal habit	Irregular veins, in masses, in nodules
Crystal system	Amorphous[1]
Cleavage	None[1]
Fracture	Conchoidal to uneven[1]
Mohs Scale hardness	5. In Mineralogy, shape and size give rise to descriptive terms applied to the typical appearance or habit of Crystals The many terms used by mineralogists A crystal system is a category of Space groups which characterize Symmetry of structures in three dimensions with Translational symmetry in three directions Cleavage, in Mineralogy, is the tendency of crystalline materials to split along definite planes creating smooth surfaces of which there are several named types In the field of Mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a Mineral is broken Conchoidal Fracture describes the way that Brittle materials break when they do not follow any natural planes of separation. The Mohs scale of mineral hardness characterizes the scratch resistance of various Minerals through the ability of a harder material to scratch a softer material 5–6. 5[1]
Luster	Subvitreous to waxy[1]
Polish luster	Vitreous to resinous[1]
Refractive index	1. Lustre (or luster) is a description of the way light interacts with the surface of a Crystal, rock, or Mineral. The refractive index (or index of Refraction) of a medium is a measure for how much the speed of light (or other waves such as sound waves is reduced inside the medium 450 (+. 020, -. 080) Mexican Opal may read as low as 1. 37, but typically reads 1. 42–1. 43[1]
Optical Properties	Single refractive, often anomalous double refractive due to strain[1]
Birefringence	none[1]
Pleochroism	None[1]
Ultraviolet fluorescence	black or white body color: inert to white to moderate light blue, green, or yellow in long and short wave. Birefringence, or double refraction, is the decomposition of a ray of Light into two rays (the ordinary ray and the extraordinary ray Pleochroism is an Optical phenomenon in which grains of a rock appear to be different colors when observed at different angles under a Petrographic microscope. Fluorescence is a Luminescence that is mostly found as an May also phosphoresce; common opal: inert to strong green or yellowish green in long and short wave, may phosphoresce; fire opal: inert to moderate greenish brown in long and short wave, may phosphoresce. [1]
Absorption spectra	green stones: 660nm, 470nm cutoff[1]
Streak	White
Specific gravity	2. Absorption spectroscopy refers to a range of techniques employing the interaction of electromagnetic radiation with matter The streak (also called powder color) of a Mineral is the Color of the powder produced when it is dragged across an unweathered surface Specific gravity is defined as the ratio of the Density of a given solid or liquid substance to the density of water at a specific temperature and pressure typically 15 (+. 08, -. 90)[1]
Diagnostic Features	darkening upon heating
Solubility	hot saltwater, bases, methanol, humic acid, hydrofluoric acid
Diaphaneity	opaque, translucent, transparent

Opal is a mineraloid gel which is deposited at relatively low temperature and may occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, and basalt. Solubility is the characteristic Physical property referring to the ability of a given substance the Solute, to dissolve in a Solvent. In Chemistry, a base is most commonly thought of as an aqueous substance that can accept Protons This refers to the Brønsted-Lowry theory of acids and Methanol, also known as methyl alcohol, carbinol, wood alcohol, wood naphtha or wood spirits, is a Chemical compound Humic acid is one of the major components of humic substances which are dark brown and major constituents of soil organic matter Humus that contributes to Soil chemical Hydrofluoric acid is a Solution of Hydrogen fluoride in Water. A gel (from the lat gelu &mdashfreezing cold ice or gelatus &mdashfrozen immobile is an apparently solid jelly-like material formed from a In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere Limonite is an ore consisting in a mixture of hydrated Iron(III oxide-hydroxide of varying composition Sandstone is a Sedimentary rock composed mainly of Sand -size Mineral or rock grains. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock.

The water content is usually between three and ten percent, but can be as high as 20%. Opal ranges from clear through white, gray, red, orange, yellow, green, shore, blue, magenta, rose, pink, slate, olive, brown, and black. Of these hues, the reds against black are the most rare and dear, whereas white and greens are the most common; these are a function of growth size into the red and infrared wavelengths—see precious opal. Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Common opal is truly amorphous, but precious opal does have a structural element. The word opal comes from the Latin opalus, by Greek opallios, and is from the same root as Sanskrit upálá[s] for "stone", originally a millstone with upárá[s] for slab. Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Sanskrit (sa संस्कृता वाक् saṃskṛtā vāk, for short sa संस्कृतम् saṃskṛtam) is a historical ^[2] (see Upal). Upal is a small town in western Xinjiang, China. Karakoram Highway Today Upal is on the Karakoram Highway, which follows Opals are also Australia's national gemstone. For a topic outline on this subject see List of basic Australia topics.

Opal is one of the mineraloids that can form or replace fossils. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. The resulting fossils, though not of any extra scientific interest, appeal to collectors.

Precious opal

Precious opal shows a variable interplay of internal colors and does have an internal structure. At the micro scale precious opal is composed of silica spheres some 150 to 300 nm in diameter in a hexagonal or cubic closed-packed lattice. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. These ordered silica spheres produce the internal colors by causing the interference and diffraction of light passing through the microstructure of opal (Klein and Hurlbut, 1985, p. In physics interference is the addition ( superposition) of two or more Waves that result in a new wave pattern Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle 444). It is the regularity of the sizes of the spheres, and of the packing of these spheres that determines the quality of precious opal. Where the distance between the regularly packed planes of spheres is approximately half the wavelength of a component of visible light, the light of that wavelength may be subject to diffraction from the grating created by the stacked planes. Diffraction is normally taken to refer to various phenomena which occur when a wave encounters an obstacle A grating is any regularly spaced collection of essentially identical Parallel, elongated elements The spacing between the planes and the orientation of planes with respect to the incident light determines the colors observed. The process can be described by Bragg's Law of diffraction. In Physics, Bragg's law is the result of experiments into the Diffraction of X-rays or neutrons off Crystal surfaces at certain angles Visible light of diffracted wavelengths cannot pass through large thicknesses of the opal. This is the basis of the optical band gap in a photonic crystal, of which opal is the best known natural example. In Solid state physics and related applied fields a band gap, also called an energy gap or bandgap, is an energy range in a solid where no electron states Photonic crystals are periodic Optical (nanostructures that are designed to affect the motion of Photons in a similar way that periodicity of a Semiconductor

Precious opal consists of spheres of silica of fairly regular size, packed into close-packed planes which are stacked together with characteristic dimensions of several hundred nm.

In addition, microfractures may be filled with secondary silica and form thin lamellae inside the opal during solidification. The term opalescence is commonly and erroneously used to describe this unique and beautiful phenomenon, which is correctly termed play of color. Opalescence is a type of Dichroism seen in highly dispersed systems with little opacity. Iridescence is an Optical phenomenon in which Hue changes with the angle from which a surface is viewed Contrarily, opalescence is correctly applied to the milky, turbid appearance of common or potch opal. Turbidity is the cloudiness or haziness of a fluid caused by individual particles ( suspended solids) that are generally invisible to the Naked eye 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 a gem. An opal doublet is a thin layer of hueladen material, backed by a swart mineral such as ironstone, basalt, or obsidian. A doublet is a type of gem composed in two sections It is sometimes used to imitate other more expensive gems Ironstone is a fine-grained heavy and compact Sedimentary rock. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Obsidian is a naturally occurring Glass formed as an extrusive Igneous rock. The darker backing emphasizes the play of color, and results in a more attractive display than a lighter potch. Given the texture of opals, they can be quite difficult to polish to a reasonable gleam. The triplet cut backs the colored material with a dark backing, and then has a domed cap of clear quartz (rock crystal) or plastic on top, which takes a high polish, and acts as a protective layer for the relatively fragile opal. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Opal doublets and triplets are not classed as precious opal.

Common opal

Besides the gemstone varieties that show a play of color, there are other kinds of common opal such as the milk opal, milky bluish to greenish (which can sometimes be of gemstone quality); resin opal, honey-yellow with a resinous luster; wood opal, caused by the replacement of the organic material in wood with opal^[3]; menilite brown or grey; hyalite, a colorless glass-clear opal sometimes called Muller's Glass; geyserite, (siliceous sinter) deposited around hot springs or geysers; and diatomite or diatomaceous earth, the accumulations of diatom shells or tests. A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. Resin, not to be confused with Rosin, is a Hydrocarbon Secretion of many Plants particularly coniferous trees. Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Menilite is a reddish-brown form of the Mineraloid Opal. It is also known as " liver opal " or leberopal, due to its color Hyalite is a form of Opal with a glassy and clear appearance which exhibits an internal play of colors and has natural inclusions Geyserite is a form of Opaline Silica that is often found around Hot springs and Geysers Botryoidal geyserite is known as Fiorite Geyserite is a form of Opaline Silica that is often found around Hot springs and Geysers Botryoidal geyserite is known as Fiorite A hot spring is a spring that is produced by the emergence of geothermally heated Groundwater from the earth's crust. A geyser is a Hot spring characterized by intermittent discharge of water ejected turbulently and accomplished by a vapour phase Diatomaceous earth (ˌdaɪətəˈmeɪʃəs ˈɝθ also known as DE, TSS, diatomite, diahydro, kieselguhr, kieselgur and Diatomaceous earth (ˌdaɪətəˈmeɪʃəs ˈɝθ also known as DE, TSS, diatomite, diahydro, kieselguhr, kieselgur and Diatoms ( Greek: (dia = "through" + (temnein = "to cut" i

Other varieties of opal

Fire opal – Fire opals are transparent to translucent opals with warm body colors yellow, orange, orange-yellow or red and they do not show any play-of-color. The most famous source of fire opals is Mexico and these opals are commonly called Mexican fire opals.

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

Boulder opal carving of a walrus, showing flashes of color from the exposed opal. The carving is 9 cm (3. 5 inches) long.

Sources of opal

Opal without play of color is very common and can be found all over the world, unlike precious opal deposits that are in greater scope found today only in Australia, U. S. , Mexico, Brazil, and Ethiopia.

Australia produces around 97% of the world’s opal. For a topic outline on this subject see List of basic Australia topics. 90% is called ‘light opal’ or white and crystal opal. White makes up 60% but not all the opal fields produce white opal; Crystal opal or pure hydrated silica makes up 30%; 8% is black and only 2% is boulder opal.

The town of Coober Pedy in South Australia is a major source of opal. Coober Pedy is a town in northern South Australia, 846 kilometres north of Adelaide on the Stuart Highway. South Australia is a state of Australia in the southern central part of the country Another Australian town, Lightning Ridge in New South Wales, is the main source of black opal, opal containing a predominantly dark background (dark-gray to blue-black displaying the play of color). Lightning Ridge is a town in north-western New South Wales, Australia, in Walgett Shire, near the southern border of Queensland. Boulder opal consists of concretions and fracture fillings in a dark siliceous ironstone matrix. Ironstone is a fine-grained heavy and compact Sedimentary rock. It is found sporadically in western Queensland, from Kynuna in the north, to Yowah and Koroit in the south. The Koroit opal field ( is an opal mining area in Paroo Shire in southwest Queensland, Australia. ^[4]

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

Fire opal is found mostly in Mexico and Mesoamerica. The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. Mesoamerica or Meso-America (Mesoamérica is a Region extending approximately from central Mexico to Honduras and Nicaragua, defined In South America opal discovered in 1930 in a city called Pedro II in Brazil is still produced. |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld In Honduras there was also some fine black opal mined from volcanic ash deposits. This opal is known for its stability.

The Virgin Valley Opal Fields Of Humboldt County in Northern Nevada produce a wide variety black, crystal, white, and fire opal. The Fire Opal mined from this locality is designated as the official gemstone of the State of Nevada. Most precious opals are wood replacements. Many specimens have a high water content, and as a result, have a greater tendency to desiccate and crack than most precious opal. Discovered in 1904 the mines are still producing gem materials in large amounts to hundreds of seasonal visitors. Three Fee Dig Mines provide the general public an opportunity to dig the gems themselves. The largest black opal in the Smithsonian Museum, possibly worth in excess of $1 million, comes from the Royal Peacock Opal Mine in the Virgin Valley.

Another source of white base opal in the United States is Spencer, Idaho. The United States of America —commonly referred to as the Spencer is a city in Clark County, Idaho, United States. The population was 38 at the 2000 census. A high percentage of the opal found there occurs in thin layers. As a result, most of the production goes into the making of doublets and triplets.

Other significant deposits of precious opal around the world can be found in the Czech Republic, Slovakia, Hungary, Turkey, Indonesia, Brazil, Honduras, Guatemala, Nicaragua and Ethiopia.

Synthetic opal

As well as occurring naturally, opals of all varieties have been synthesized experimentally and commercially. The discovery of the ordered sphere structure of precious opal led to its synthesis by Pierre Gilson in 1974 (Klein and Hurlbut, 1985, p. 528). The resulting material is distinguishable from natural opal by its regularity; under magnification, the patches of color are seen to be arranged in a "lizard skin" or "chicken wire" pattern. Synthetics are further distinguished from naturals by the former's lack of fluorescence under UV light. Fluorescence is a Luminescence that is mostly found as an Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays Synthetics are also generally lower in density and are often highly porous; some may even stick to the tongue.

Two notable producers of synthetic opal are the companies Kyocera and Inamori of Japan. is a Japanese company based in Kyoto, Japan. The company was founded as in 1959 by Kazuo Inamori. For a topic outline on this subject see List of basic Japan topics. Most so-called synthetics, however, are more correctly termed imitations, as they contain substances not found in natural opal (e. g. , plastic stabilizers). The imitation opals seen in vintage jewellery are often "Slocum Stone" consisting of laminated glass with bits of foil interspersed.

The Hamamatsu Photonics Group will utilise the International Space Station's Japanese Experiment Module in 2006 to grow perfect crystalline opals in microgravity over four months, as compared with five million years for naturals. The Japanese Experiment Module (JEM ( Japanese: Kibō きぼう Hope is a Japanese science module for the International Space Station Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Such opals will be the object of study and elements for optical filters, displays, and data storage. ^[5][6]

Local atomic structure of opals

The lattice of spheres of opal that cause the interference with light are several hundred times larger than the fundamental structure of crystalline silica. As a mineraloid, there is no unit cell that describes the structure of opal. A mineraloid is a Mineral -like substance that does not demonstrate Crystallinity. In Mineralogy and Crystallography, a crystal structure is a unique arrangement of Atoms in a Crystal. Nevertheless, opals can be roughly divided into those that show no signs of crystalline order—i. e. , amorphous opal—and those that show signs of the beginning of crystalline order, commonly termed cryptocrystalline or microcrystalline opal (Graetsch, 1994). An amorphous solid is a Solid in which there is no Long-range order of the positions of the Atoms (Solids in which there is long-range atomic order are Cryptocrystalline is a rock texture which is so finely crystalline being made up of such minute Crystals that its crystalline nature is only vaguely revealed Dehydration experiments and infrared spectroscopy have shown that most of the H₂O in the formula of SiO₂·nH₂O of opals is present in the familiar form of clusters of molecular water. Infrared spectroscopy (IR spectroscopy is the subset of Spectroscopy that deals with the Infrared region of the Electromagnetic spectrum. Isolated water molecules, and silanols, structures such as Si-O-H, generally form a lesser proportion of the total and can reside near the surface or in defects inside the opal. Silanols are compounds containing Silicon Atoms to which Hydroxy Substituents bond directly

The structure of low-pressure polymorphs of anhydrous silica consist of frameworks of fully-corner bonded tetrahedra of SiO₄. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide The higher temperature polymorphs of silica cristobalite and tridymite are frequently the first to crystallize from amorphous anhydrous silica, and the local structures of microcrystalline opals also appear to be closer to that of cristobalite and tridymite than to quartz. The mineral cristobalite is a high-temperature polymorph of Quartz and Tridymite. Tridymite is a high-temperature polymorph of Quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal Triclinic crystals or scales The mineral cristobalite is a high-temperature polymorph of Quartz and Tridymite. Tridymite is a high-temperature polymorph of Quartz and usually occurs as minute tabular white or colorless pseudo-hexagonal Triclinic crystals or scales The structures of tridymite and cristobalite are closely related and can be described as hexagonal and cubic close-packed layers. It is therefore possible to have intermediate structures in which the layers are not regularly stacked.

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

Microcrystalline opal

Opal-CT has been interpreted as consisting of clusters of stacking of cristobalite and tridymite over very short length scales. The spheres of opal in opal-CT are themselves made up of tiny microcrystalline blades of cristobalite and tridymite. Opal-CT has occasionally been further subdivided in the literature. Water content may be as high as 10 wt%. Lussatite is a synonym. Lussatite Is described in Dana's Textbook of Mineralogy 4th ed

Opal-C is interpreted as consisting of localized order of α-cristobalite with a lot of stacking disorder. Typical water content is about 1. 5wt%. Lussatine is a synonym.

Non-crystalline opal

Two broad categories of non-crystalline opals, sometimes just referred to as opal-A, have been proposed

Opal-AG: Aggregated spheres of silica, with water filling the space in between. Precious opal and potch opal are generally varieties of this, the difference being in the regularity of the sizes of the spheres and their packing.

Opal-AN: Water-containing amorphous silica-glass. Hyalite is a synonym. Hyalite is a form of Opal with a glassy and clear appearance which exhibits an internal play of colors and has natural inclusions

Non-crystalline silica in siliceous sediments is reported to gradually 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 stacking disorder is removed (Cady et al., 1996)PDF (2. In Geology and Oceanography, diagenesis is any chemical physical or biological change undergone by a Sediment after its initial deposition and during Sedimentary rock is one of the three main rock types (the others being igneous and Metamorphic rock) 03 MiB). A mebibyte (a contraction of me ga bi nary byte) is a unit of Information or Computer storage, abbreviated MiB.

Historical superstitions

In the Middle Ages, opal was considered a stone that could provide great luck because it was believed to possess all the virtues of each gemstone whose color was represented in the color spectrum of the opal. ^[7] However, modern superstition attributes bad luck to the stone, though some believe this is avoided if opal is the owner's birthstone (that is, the owner was born in October) or if the stone is a gift. Birthday is the name given to the date of the anniversary of a person's birth October events and holidays Children's Book Week ( England) - First Week of October National Day ( China People's Republic Even under the last czar at the beginning of the 20th century, it was believed that when a Russian of any sex, of any rank, saw an opal, amongst other goods offered for sale, he or she would not buy anything more, since, in the judgement of subjects of the tzar, the opal embodied the evil eye. ^[7] It's possible that the stone's extreme fragility (when compared to other gemstones) has contributed to this bad reputation.

Opals in popular culture

The opal is the official gemstone of South Australia, The Commonwealth of Australia and Nevada and the Australia's women's national team in basketball is nicknamed The Opals. A gemstone or gem, also called a precious or semi-precious stone, is a piece of attractive Mineral, which &mdash when cut and polished &mdash South Australia is a state of Australia in the southern central part of the country For a topic outline on this subject see List of basic Australia topics. Nevada ( is a state located in the western region of the United States of America. The Australia Women's National Basketball Team (nicknamed The Opals) is the women's National Basketball team for Australia. Basketball is a team Sport in which two teams of five active players each try to score points against one another by propelling a ball through a 10 feet (3 m

Opal is the traditional birthstone of the month of October. Early civilizations such as India and Babylon have attributed gemstones with magical properties

Famous opals

• The Andamooka Opal, presented to Queen Elizabeth II, also known as the Queen's Opal
• The Aurora Australis Opal, considered to be the most valuable black opal
• The Black Prince Opal, originally known as Harlequin Prince
• The Empress of Australia Opal
• The Fire Queen Opal
• The Flame Queen Opal
• The Flamingo Opal
• The Halley's Comet Opal, the world's largest uncut black opal
• The Jupiter Five Opal
• The Olympic Australis Opal, reported to be the largest and most valuable uncut gem opal ever found
• The Pride of Australia Opal, also known as the Red Emperor Opal
• The Red Admiral Opal, also known as the Butterfly Stone

See also

• Optical phenomena
• Upal

References

• Graetsch, H. , "Structural Characteristics of opaline and microcrystalline silica minerals", "Silica, physical behavior, geochemistry and materials applications". Reviews in Mineralogy, Vol. 29, 1994. Editors PJ Heaney, CT Prewitt, GV Gibbs, Mineralogical Society of America,
• Klein, Cornelis, and Hurlbut, Cornelius S. ; 1985, Manual of Mineralogy, 20th ed. , ISBN 0-471-80580-7

External links

• Pictures and information on famous opals
• Mindat.org: Opal: Precious Opal Gallery, Opal Gallery
• Farlang Opal Hist. References: localities, anecdotes by Theophrastus, Isaac Newton, Georg Agricola etc. Theophrastus ( Greek:; 371 – c 287 BC a Greek native of Eressos in Lesbos, was the successor of Aristotle in the Peripatetic Sir Isaac Newton, FRS (ˈnjuːtən 4 January 1643 31 March 1727) Biography Early years See also Isaac Newton's early life and achievements Georgius Agricola ( March 24, 1494 – November 21, 1555) was a German scholar and scientist
• Berkeley Agates and Opals: great photos
• ICA's Opal Page: International Colored Stone Association
• Webmineral: Opal: crystallographic and mineralogical info
• High quality images of opal jewellery