Opal chemical composition

Composition. Hydrous silicon dioxide. The water can range from 3% to 21% of the total weight, but is usually between 6% to 10%. Color. Colorless, white, yellow, orange, red, purple, blue, green, gray, brown, and black. These are some of the base colors of Opal.

Opal chemical composition. Beryl (/ ˈ b ɛr əl / BERR-əl) is a mineral composed of beryllium aluminium silicate with the chemical formula Be 3 Al 2 Si 6 O 18. Well-known varieties of beryl include emerald and aquamarine.Naturally occurring, hexagonal crystals of beryl can be up to several meters in size, but terminated crystals are relatively rare. Pure beryl is colorless, but it is frequently …

Many times, your Opal may completely turn transparent or clear. This happens mainly because of the change in the water composition of the stone. The majority of the time, the color play of an Opal is disturbed due to fluctuations in its water content. At other times, this may happen due to the accumulation of dirt, grime, or harsh cleaning.

Opal is one of the very few amorphous minerals, which means that it has no crystal structure. Apart from being amorphous, opal has some more specific features.Jun 11, 2022 ... It has the same chemical composition as natural Opal without the water content. ... These are look-like Opals, but they differ from the natural ...Tiger's eye (also called tiger eye) is a chatoyant gemstone that is usually a metamorphic rock with a golden to red-brown colour and a silky lustre.As members of the quartz group, tiger's eye and the related blue-coloured mineral hawk's eye gain their silky, lustrous appearance from the parallel intergrowth of quartz crystals and altered amphibole fibres …Opal is a mineraloid because it is amorphous hydrated silica. Despite its mineral-like properties, opal’s chemical structure is hydrated with varied water concentration. Because of this variance, the stone’s structure isn’t fixed or organized and thus, qualifies as a mineraloid.Lab Created Opal Lab Created Aurora Opal Lab Created Bello Opal Lab Created Gilson Opal Lab Created Jelly Opal Lab Created ... Chemical Composition: Same. Add to Wishlist $ 19.90 – $ 130.00 Select options. Lab Created Hydrothermal Emerald, Asscher. GEMSTONE DETAIL Origin: Grown in Lab by Hydrothermal method. One of the best …1. a mineral made of oxidized hydrogen. 2. an item that is solid like a mineral, has definite chemical composition, and shows distinctive physical properties, but is not naturally occurring. 3. silicate mineral consisting solely of silicon and oxygen, with silicon-oxygen tetrahedra bonded in a complex three-dimensional network.

Buy best quality pandora beads synthetic opal for sale online, We have a huge range of pandora beads synthetic opal on sale at very best prices. ... Grown in Lab Chemical Composition: 80% silica & 20% resin Dimensions: 1.25mm to 50mm Grade: AAA Clarity: Opaque Shape: Can do in all $ 37.00 – $ 660.00Fire Opal is rare compared to other colors because of its chemical structure and depositional environment. To illustrate, opal stones reflect a red color when white light refracts upon sections of larger silica spheres. And the composition of larger silica spheres in an opal stone is due to a less common depositional environment.Opal is a hydrated amorphous form of silica (SiO 2 · n H 2 O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals. It is deposited at a relatively low temperature and may occur ...Opal is a hydrous silicon dioxide with a chemical composition of SiO2.nH2O in terms of mineralogy. It’s amorphous, meaning it doesn’t have a crystalline …Common opal is a mineraloid. It is an amorphous silica with a chemical composition of SiO 2. nH 2 O. It has a conchoidal fracture that is characteristic of an amorphous glass. Precious Opal is a mineraloid. The play-of-color in opal is produced when light travels through a three-dimensional array of tiny silica spheres within the material. The chemical composition of perfume is generally made up of two components: a base substance and various scented oils. Bases are usually made of a mixture of water (H2O) and ethyl alcohol (C2H6O), while the chemical composition of the oils ...Jan 29, 2023 · Take a look at examples of each of the beautiful birthstone minerals: January Birthstone – Garnet [ Chemical Formula X3Y2(SiO4)3] Spessartine Garnet Crystal (ButtShark) Color: any, but birthstone is usually red. Hardness: 6.5 to 7.5. Crystal Habit: Cubic or Rhombic Dodecahedron. The traditional birthstone for January is garnet.

Obsidian is an igneous rock that forms when molten rock material cools so rapidly that atoms are unable to arrange themselves into a crystalline structure. It is an amorphous material known as a " mineraloid ." The result is a volcanic glass with a smooth uniform texture that breaks with a conchoidal fracture (see photo).Buy best quality pandora beads synthetic opal for sale online, We have a huge range of pandora beads synthetic opal on sale at very best prices. ... Grown in Lab Chemical Composition: 80% silica & 20% resin Dimensions: 1.2mm to 50mm Grade: AAA Clarity: Opaque Shape: Can do in all.Now we're getting into the heart of gem classification. The vast majority of gems are minerals. Both chemical makeup and molecular structure define the mineral species. Chemical Makeup. Chemical makeup" refers to the atoms contained within the mineral. Diamond, for example, has the simplest chemical makeup. Carbon (C) is the only …Chemical Composition. Opalite can refer to one of two stones. One is natural, commonly referred to as common opal, a hydrated silicon dioxide. This type does not have play-of-color, which is normally associated with opal. The other opalite is artificially made using resin, glass, and metal.General Opal Information : Chemical Formula: SiO2•n(H2O) Composition: Molecular Weight = 87.11 gm Silicon 32.24 % Si 68.98 % SiO 2 Hydrogen 3.47 % H 31.02 % H 2 O Oxygen 64.29 % O _____ _____ 100.00 % 100.00 % = TOTAL OXIDE: Empirical Formula: SiO 2 •1.5(H 2 O) Environment:

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Opalescence Boost in-office power whitener is a chemically activated gel that provides brighter, whiter teeth after about an hour in the dental chair. The powerful 40% hydrogen peroxide gel is chemically activated, so it doesn’t require a hot, uncomfortable light to work. Using the unique double-syringe configuration, the clinician activates ...October’s birthstone is the opal, a gemstone that’s been prized for its beauty and rarity for centuries. In this article, we’ll take a closer look at what makes opals so special, how they’re formed, and what to look for when shopping for an...Specific gravities are expressed in decimal numbers, for example, 4.00 for corundum, 3.52 for diamond , and 2.72 for quartz. Zircon, one of the densest of all gemstones, may have a specific gravity as high as 4.73! Specific gravity is an important tool in gemstone identification that is useful for the gem buyer as well as the gemologist.The opal forms in pre-existing clay or sandstone. This material is frequently dyed. Doublets & Triplets: These assembled stones are not considered natural opals, although they do contain a layer of natural opal. Common Opal or Potch: These are varieties of opal that do not show a play-of-color. Although they share the same chemical composition ... Jasper, an aggregate of microgranular quartz and/or cryptocrystalline chalcedony and other mineral phases, is an opaque, impure variety of silica, usually red, yellow, brown or green in color; and rarely blue.The common red color is due to iron(III) inclusions.Jasper breaks with a smooth surface and is used for ornamentation or as a gemstone.It can be highly …

Chemical Composition: SiO2 – nH2O Hydrated Silicon Dioxide. Hardness: 5.5-6. Opal Name Etymology. Experts contend that opal gets its name from the Sanskrit word upala, which simply means precious stone (yeah, not overly creative!). Even with such a basic beginning some of the greatest Historians wrote of opals including Pliny the Elder.Chemical Composition: Beryllium aluminum silicate. The beryl family is considered to be one of the most important of gemstone groups. ... Opal gemstones typically contain around three to thirty percent water and can be classified into three main sub-varieties: Precious opal, common opal and fire opal. Precious opal will typically …Chalcedony (/ k æ l ˈ s ɛ d ə n i / kal-SED-ə-nee, or / ˈ k æ l s ə ˌ d oʊ n i / KAL-sə-doh-nee) is a cryptocrystalline form of silica, composed of very fine intergrowths of quartz and moganite. These are both silica minerals, but they differ in that quartz has a trigonal crystal structure, while moganite is monoclinic.Chalcedony's standard chemical structure …Feb 1, 2000 · Class: semiprecious Origin of Name: from the Latin aqua marina (sea water) Color: blue, blue-green, green Chemical Composition: beryllium aluminum silicate Crystal System: hexagonal Hardness: 7.5 ... So whereas the chemical composition of quartz is Si O2, the composition of opal is Si02 H20. I'm not a chemist, but I don't believe that changes easily ...Opal and Amber are not classified as minerals but rather as mineraloids. This classification is based upon the fact that these mineraloids Olack an orderly arrangement of atoms occur naturally but can be man-made as well meet all other criteria but are in a liquid state O meet all other criteria but lack a definite chemical composition. Petro chemicals. Petro. chemicals. With ISO 9001:2015, ISO 14001:2015 and BS OHSAS 18001:2007 accreditations, GAIL is committed towards producing a quality product with creating, maintaining and ensuring a safe and clean environment. GAIL’s polymer products are environment-friendly and fully recyclable. GAIL provides a wide choice of grades ...Feb 14, 2020 ... Chemical Composition. Opal shares its chemical composition with quartz crystal. SiO2, Silicon Dioxide. Opal also contains some amount of water.A synthetic gem material is one that is made in a laboratory, but which shares virtually all chemical, optical, and physical characteristics of its natural mineral counterpart, though in some cases, namely synthetic turquoise and synthetic opal, additional compounds can be present.

Composition: Molecular Weight = 87.11 gm Silicon 32.24 % Si 68.98 % SiO 2 Hydrogen 3.47 % H 31.02 % H 2 O Oxygen 64.29 % O ______ ______ 100.00 % 100.00 % = …

An opal is a gem, a semi-precious stone that comes in many shimmery, partly translucent colors. If your birthday is in October, an opal is your birthstone. An ...Artificial materials mimicking the opal structure not only give appealing colors but also offer unique optical, mechanical, and other physical properties. In this issue of ACS Central Science, Shen and coauthors draw inspiration from the opal structure to synthesize metal–organic frameworks (MOFs) using a 3D-ordered template replicating a ...Marking of product made of Melamine. Melamine / ˈ m ɛ l ə m iː n / ⓘ is an organic compound with the formula C 3 H 6 N 6.This white solid is a trimer of cyanamide, with a 1,3,5-triazine skeleton. Like cyanamide, it contains 67% nitrogen by mass, and its derivatives have fire-retardant properties due to its release of nitrogen gas when burned …There is plenty of pore space and water for this to happen, and plenty of chemical energy being released by crystallization as well as by the breakdown of organic matter in the ooze. The first product of this activity is hydrated silica ( opal ) called opal-CT because it resembles cristobalite (C) and tridymite (T) in X-ray studies.Opal definition, a mineral, an amorphous form of silica, SiO2 with some ... Composition: hydrated silica. Formula: SiO 2 . n H 2 O. Origin of opal. 1. C16: from ...Chemical Symbol: SiO 2 nH 2 O Name: There is some uncertainty around the origin of the word opal - it may come from the Greek opallos meaning 'to see a change (of colour)' or may be Sanskrit for …Common glass types and composition of commercial glasses. Glass Composition, Glass Types . Related sites: Glass Properties on GlobalSpec, GlassOnWeb, MatWeb, Glass Global A general overview about glass art, history, science, literature, social studies, and technology is available at the Corning Museum of Glass (view as PDF, 1.8 MB). Schott …About Tanzanite. Found in just one place on earth, tanzanite is a relatively recent discovery. Tiffany & Co named this blue-violet variety of zoisite in honor of Tanzania, where it was first unearthed in 1967. Because the crystals show different colors depending on the viewing direction, cutters can fashion gems with a range of color from ...Chemical Formula: SiO 2: Composition: Silicon dioxide, usually with impurities of iron oxides or organic substances. Color: Brown, yellow, orange, red, green, or blue. ... - Opal Jasper is a form of Brecciated Jasper in which the cementing material is Opal.Opalite is a name used in two different ways: 1. As a synonym for common opal (natural opal that does not exhibit play-of-color). 2. As a marketing term used for numerous man-made materials that have an opal-like appearance but are composed of plastic or glass. Natural Opalite: Most natural common opal is not as colorful as the gems in the top ...

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Sunstone is also known as "heliolite" and more commonly "aventurescent feldspar." It is cut into cabochons, beads, and small sculptures. The most transparent pieces are used to produce faceted stones. Sunstone is popular with innovative jewelry designers and is especially popular in the geographic areas where it is commercially mined.The early synthesis of opal attempted to produce synthetic opal with this chemical composition, however it is likely that at some stage during the refinement of the manufacturing process that two modifications were made. First, most of the water was removed from the synthesised opal. The second was the introduction of a suitable 'stabilizing ...Opal stored in water should not be taken out of the water for more than several minutes at a time. Cutting or polishing Opals, especially Opals from localities notorious for crazing, is a risky process; it is a matter of chance if the Opals will craze or not. ... Chemical Formula: SiO 2 · nH 2 O: Composition: Hydrous silicon dioxide. The water ...The chemical composition which was given by Tschermak in 1884 for this dravite approximately corresponds to the formula NaMg 3 (Al,Mg) 6 B 3 Si 6 O 27 (OH), which is in good agreement (except for the OH content) with the endmember formula of dravite as known today. Dravite varieties include the deep green chromium dravite and the vanadium dravite.The aesthetic properties of the opal glass were determined by studying the transmittance of visible light in the 400 nm to 700 nm range. The basic chemical composition of opal glass was 52.9 wt ...Black opal is a variety of opal that shares the same chemical composition and characteristics as all opals. Opal is a colorful class of gemstones that range in color from white to orange to black. The most valued opals showcase an optical phenomenon called “play of color,” which is a feature only seen in opal gemstones. Earlier work by some of us2 supported these conclusions, and a comprehensive re-examination of natural opals has confirmed that the structure can vary from almost perfect α-cristobalite to ... ITO is a mixed oxide of indium and tin with a melting point in the range 1526–1926 °C (1800–2200 K, 2800–3500 °F), depending on composition. The most commonly used material is an oxide of a composition of ca. In 4 Sn. The material is a n-type semiconductor with a large bandgap of around 4 eV. [1] ITO is both transparent to visible light ...Opal, silica mineral extensively used as a gemstone, a submicrocrystalline variety of cristobalite. In ancient times opal was included among the noble gems and was ranked second only to emerald by the Romans.Jun 20, 2023 ... Chemical Composition: What Lies Beneath ... Moonstones are primarily composed of orthoclase feldspar minerals with scattered deposits of albite ...Jones, J.B. and E.R. Segnit (1971), The nature of opal. I Nomenclature and constituent phases. Journal of the Geological Society of Australia: 18: 57-68. ….

Jones, J.B. and E.R. Segnit (1971), The nature of opal. I Nomenclature and constituent phases. Journal of the Geological Society of Australia: 18: 57-68. Peruvian Opal is the national stone of Peru and it is relatively rare and can only be found in the Andes mountains. Its internal crystalline composition is random, meaning this gemstone lacks the colour play or fire of a usual Opal. Peruvian Opal is a sedimentary rock formed at low temperature from an igneous rock with high silica content. The name "opalite" is used for a wide variety of man-made materials. Many of them would be properly labeled "imitation opal" or "opal simulant" in a retail setting. They do not …In simpler terms, an opal is a solid gemstone without a clearly defined shape or form that is solidified from chemical silicon dioxide. There are two types of ...Opalite is a name used in two different ways: 1. As a synonym for common opal (natural opal that does not exhibit play-of-color). 2. As a marketing term used for numerous man-made materials that have an opal-like appearance but are composed of plastic or glass. Natural Opalite: Most natural common opal is not as colorful as the gems in the top ...Aug 23, 2019 ... 1. Chemical Composition. Opal. This gem is made up of tiny silica spheres, formed when silica-rich water enters into the deep voids and cracks ...Apr 23, 2023 · Chert is a fine-grained sedimentary rock composed of quartz (SiO2) that is microcrystalline or cryptocrystalline quartz. It is usually organic rock but also occur inorganically as a chemical precipitate or a diagenetic replacement. It occurs as nodules, concretionary masses, and as layered deposits. Name origin: Term is used to refer generally ... Under (Atmospheric) Pressure - The pressure of the atmosphere is immense, and it grows as you get closer to the planet's surface. Learn about pressure and how it affects weather. Advertisement We've discussed the origins and chemical compos... Opal chemical composition, In the upper part of QAPF classification of plutonic rocks (Streckeisen, 1976), the granite field is defined by the modal composition of quartz (Q 20 – 60 %) and the P/(P + A) ratio between 10 and 65. The granite field comprises two sub-fields: syenogranite and monzogranite. Only rocks projecting within the syenogranite are considered granites in …, Tendency to chemical cement. Ash: unconsolidated fragments under. 4 mm. Tuff: consolidated ash. Volcanic Breccia: angular fragments over 4 mm. Agglomerate: large proportion (>25%) of bombs. These rocks are classified on the proportions of vitric, crystal (mineral), or lithic material they contain, for example, "vitric lithic ash," or "crystal ..., soda-lime glass, most common form of glass produced. It is composed of about 70 percent silica (silicon dioxide), 15 percent soda (sodium oxide), and 9 percent lime (calcium oxide), with much smaller amounts of various other compounds.The soda serves as a flux to lower the temperature at which the silica melts, and the lime acts as a stabilizer for the silica., Chert. Chert ( / ˈtʃɜːrt /) is a hard, fine-grained sedimentary rock composed of microcrystalline or cryptocrystalline quartz, [1] the mineral form of silicon dioxide (SiO 2 ). [2] Chert is characteristically of biological origin, but may also occur inorganically as a chemical precipitate or a diagenetic replacement, as in petrified wood., synthetic opal chemical composition: sio2.nh2o+resin Many countries manufacture opals as it is a valuable gemstone, so unfortunately we will be expecting more synthetic opals to come on line. To our knowledge China and Thailand are constantly trying to manufacture new products for this market to catch the unsuspecting opal buyer. , What Is A Green Opal? On a chemical level, what is green opal? Well, like other opals, green opals are a hydrated amorphous form of silica (hence their chemical formula, SiO2·nH2O). They have more or less the same chemical composition as minerals like quartz, but with a more disorganized internal structure. , Jan 20, 2023 ... The soil is a chemically rich and complex environment. Many natural molecules can be suspected to contribute to the transformation of the silica ..., Aug 23, 2019 ... 1. Chemical Composition. Opal. This gem is made up of tiny silica spheres, formed when silica-rich water enters into the deep voids and cracks ..., Diamonds: Learn about the properties of diamond, its many uses, and diamond discoveries. Unakite is a pink and green metamorphic rock and a popular gem material. It consists of pistachio-green epidote, pink orthoclase and quartz. It is also used as a construction material, an architectural stone, and a lapidary material., Sep 4, 2023 ... Both the common and precious varieties of opal consist of hydrous silicon dioxide. Despite having a composition similar to that of quartz ( ..., So whereas the chemical composition of quartz is Si O2, the composition of opal is Si02 H20. I'm not a chemist, but I don't believe that changes easily ..., Diamond simulants are materials that look like diamond, but they have different chemical compositions. Diamond simulants can be natural materials such as colorless zircon or sapphire. More often they are man-made materials such as cubic zirconia (ZrO 2), moissanite (SiC), YAG (yttrium aluminum garnet Y 3 Al 5 O 12), or strontium titanate …, The typical chemical composition of oven-dried diatomaceous earth is 80–90% silica, with 2–4% alumina (attributed mostly to clay minerals), and 0.5–2% iron oxide. ... Diatomite forms by the accumulation of the amorphous silica (opal, ..., Fire opal is named for its color and does not display opalescence. It can range in color from yellow to red. It is usually milky, but the best examples can be transparent. Opals are found in the veins and cavities of igneous or sedimentary rock. The best quality opals are found in Australia, but the gemstone is also found in Brazil, Mexico ... , Fire opal is named for its color and does not display opalescence. It can range in color from yellow to red. It is usually milky, but the best examples can be transparent. Opals are found in the veins and cavities of igneous or sedimentary rock. The best quality opals are found in Australia, but the gemstone is also found in Brazil, Mexico ..., Opal is a hydrous silica composed of predominantly silicon dioxide and water. The chemical composition of opal is normally described by the general formula SiO2.nH2O. The formula indicates that opal contains water and the value of ‘n’ is variable so the water content is variable and is known to range widely., Agate (/ ˈ æ ɡ ɪ t /) is the banded variety of chalcedony, which comes in a wide variety of colors. Agates are primarily formed within volcanic and metamorphic rocks.The ornamental use of agate was common in Ancient Greece, in assorted jewelry and in the seal stones of Greek warriors, while bead necklaces with pierced and polished agate date back to the 3rd millennium BCE in the Indus ..., Lichtenberg figure: high-voltage dielectric breakdown in an acrylic polymer block. Poly(methyl methacrylate) (PMMA) is the synthetic polymer derived from methyl methacrylate.It is used as an engineering plastic, and it is a transparent thermoplastic.PMMA is also known as acrylic, acrylic glass, as well as by the trade …, Iolite (also called Dichroite or Cordierite) is a transparent, violet-blue, light blue, blue, rich blue-violet stone. It is a blue silicate mineral that occurs as crystals or grains in igneous rocks, only as a result of contamination of the magma by aluminous sediment. Its chemical composition is Magnesium Aluminum Silicate (Mg 2 Al 3 O). , The chemical composition of Peruvian opal includes oxygen, hydrogen, and silicon while silicon present in the highest content. You can find Peruvian opal in two types – blue Peruvian opal and pink Peruvian opal. Due to high water content, blue Peruvian opal comes in the cool blue shade and is also sensitive to heat. Exposing these opals to ..., Class: semiprecious Origin of Name: from the Latin aqua marina (sea water) Color: blue, blue-green, green Chemical Composition: beryllium aluminum silicate Crystal System: hexagonal Hardness: 7.5 ..., General Opal Information : Chemical Formula: SiO2•n(H2O) Composition: Molecular Weight = 87.11 gm Silicon 32.24 % Si 68.98 % SiO 2 Hydrogen 3.47 % H 31.02 % H 2 O Oxygen 64. ... Opal Image: Images: Opal. Comments: Colorful white opal on a sandstone matrix., such creation that is an equal marvel to the eye as it is to geological science is that of precious opal. Few other gemstones can attribute their creation ..., Opal is a hardened gel of silica and water (usually 6 – 10%). Its physical properties vary with differences in its structure and water content. Unlike other minerals opal is amorphous, with no definite crystal structure. Opal is a common mineral, found in many countries and various geological environments. , Opal is a mineraloid, an amorphous material without a crystalline structure. It is composed of tiny spheres of amorphous silica with a chemical composition of SiO 2. nH 2 O. The tiny silica spheres are translucent to transparent and allow the passage of light. In common opal the spheres are of various sizes and arranged in an irregular pattern ..., Opalite versus opal. Opal is 100% natural. It is made of water and silicon dioxide. Water goes through rock crevasses as it flows down the earth. When it evaporates, the silica dries out and becomes opal. Opal has a beautiful display of colors, as well as some fascinating patterns – whether symmetrical or asymmetrical., 19000; H, premous opal, Coober Pedy, South Australia, No. 17015. ... though its composition would suggest the possibility of a semi -conductor of ionic formula Ti<+(As 2 )•-. ... , Agate—a spectacular form of SiO2 and a famous gemstone—is commonly characterized as banded chalcedony. In detail, chalcedony layers in agates can be intergrown or intercalated with macrocrystalline quartz, quartzine, opal-A, opal-CT, cristobalite and/or moganite. In addition, agates often contain considerable amounts of mineral inclusions and water as both interstitial molecular H2O and ..., Earlier work by some of us2 supported these conclusions, and a comprehensive re-examination of natural opals has confirmed that the structure can vary from almost perfect α-cristobalite to ..., For example, the hydrous mineral Opal has a loosely defined composition with an inconsistent amount of water in its structure, thus its chemical formula is written as "SiO 2 · nH 2 O". Some minerals, such as Torbernite, have a varying amount of water within fixed limits. The chemical formula for Torbernite is "Cu(UO 2)(PO 4) 2 · 8-12H 2 O"., Article by: Hobart M. King, PhD, RPG. Common opal is a mineraloid. It is an amorphous silica with a chemical composition of SiO 2. nH 2 O. It has a conchoidal fracture that is characteristic of an amorphous glass. …, Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. ⓘ Old Coocoran rush (Coocoran A) Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. ⓘ Olga's rush, In reality, all of the so-called ‘synthetic’ opals are, in fact, imitation opals-for by strict gemmological definition their chemical compositions differ (to variable extents) …