What Is Opal and What Is It Made Of

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Opal is a non-crystalline form of mineral silica. Opal is related to the more common crystalline cousins such as quartz and agate. Opal differs as it is formed from amorphous lumps of silica rather than that from naturally faceted crystals. The chemical composition of opal is SiO2H2O, silicon dioxide combined with water (an opal stone may contain up to 30% water.) Opal’s Moh’s hardness rating is measured at 6.0 to 6.5 on the scale similar in hardness to quartz. Most opal is more than 65 million to 145 million years old and is found in the Cretaceous layer of rock which was during the period when dinosaurs roamed the earth.

Opal tends to be found near the earth’s surface in areas where ancient geothermal hot springs once flowed. The minerals bubbled up from beneath the surface of the earth and slowly over centuries lined the walls of cavities in the bedrock. More than 90% of the world’s quality gem opals come from Southern Australia, although it can be found in other parts of the world such as Ethiopia, Brazil, Mexico, Czechoslovakia and Nevada. All black opal comes exclusively from Australia.

To define opal in layman terms, it is a solid gem mineraloid (has mineral characteristics, but is not one) that is solidified from the chemical silicon dioxide, which come from cavities in decaying vegetation, wood, and bones. In science mode, opal is known as SiO2·nH2O, mixing silicon dioxide with water. Unlike other gems, opal comes in many varieties – white, blue, red, black, and even colorless. Its most unique character is that it displays all the colors of the spectrum resulting from the interference and diffraction of light passing through it. In other words, the bright rainbow look of opal, as they appear to the when seen, will move and change dramatically depending on the angle at which the stone is viewed.

Opal Varieties

There are two main varieties of opal - precious and common. Precious opals exhibit the characteristic called “play-of-color,” and are comparatively rare. Common opal is dull and valueless and occurs in abundance throughout the world. Common opal does not exhibit a play of color. When common opal is found in association with precious opal, it is known as potch. About 95% of all opal mined from the opal fields are common or potch, basically one colored. The remaining 5% has some color, but about 95% of it is of mediocre grade. Therefore, only approximately 0.25% has any real value at all. The other kinds of opal include Fire Opal, which is transparent to translucent, a blue opal known as Peruvian Opal, and Girasol opal, which comes from Mexico mainly, and exhibits a bluish glow or sheen that follows the light source around which is not a play of color.

Opal Is Sedimentary

Opal is one of the few gemstones that are sedimentary in origin. Opal still contains 6 to 10 percent water, a remnant of that ancient sea. Gold panners in Australia found the first few pieces of precious opal in 1863. A large percentage of the world’s stable commercial opal comes from Australia, and there are three distinctive regions where opal comes from. These are Lightning Ridge (the home of black opal) the South Australian fields Coober Pedy, Mintabie, Lambina and Andamooka (the main sources of light base opal) and the Queensland fields, where boulder opal originates.

Opalescence

The most striking feature of opal is the ability to refract and reflect specific wavelengths of colours. In fact, the term “opalescence” was coined to describe this phenomenon. The size and spacing of the amorphous spheres of silica within the stone refracts specific wavelengths of light; each sphere refracting a single, pure spectral colour much like the droplets of water in a rainbow. The interplay of these pure wavelengths of light gives opal its unique visual appeal and makes it one of the most sought-after gemstones in the world.

History Of Opal

Opals contain the wonders of the skies - sparkling rainbows, fireworks and lightning. Like the sky the opal colours shift and flash with movement, the combination of colours and patterns means every opal is unique. Black opal was first discovered in Australia in the late 1800s. Before its discovery the world was only aware of crystal opal which was typically mined in Eastern Europe. Many royal families throughout history have treasured opal particularly in Europe and Africa. The oldest recorded opal was found by the famous archaeologist Louis Leakey who found six thousand year old opal artifacts in a cave in Kenya! The Roman historian Pliny rightfully described opal as the queen of gems, as opal is a combination of the beauty of all other gems: “There is in them a softer fire than the ruby, there is the brilliant purple of the amethyst, and the sea green of the emerald - all shining together in incredible union. Some by their splendour rival the colours of the painters, others the flame of burning sulphur or of fire quickened by oil.”

Opals have been popular with some of the greatest names in history including Cleopatra and Marc Anthony. One of Marc Anthony’s fellow Roman senators owned an opal stone that reminded Marc of Cleopatra so much that he had to have it. When the Senator refused to sell it to him he sent him into exile.The French Emperor Napoleon was more successful giving Josephine a beautiful opal with brilliant red flashes called “The burning of Troy,” making her his Helen.

Opals were also famous in literature. Shakespeare likening the opals play of colour to play of mind in the most famous use of gemstone symbolism in literature. In Twelfth Night, he writes: “Now the melancholy God protect thee, and the tailor make thy garments of changeable taffeta, for thy mind is opal.” For a few centuries opals seemed to disappear from history. However in modern times Queen Victoria reignited interest in the gemstone. Queen Victoria loved opals and often gave them as wedding presents. She and her daughters created a fashion trend for the wearing of Opal.

Queen Victoria was one of the first to appreciate opals from an exciting new source: Australia. The story of Australian opal begins more than 100 million years ago, when the deserts of central Australia were a great Inland Sea, with silica-laden sediment deposited around its shoreline. After the sea receded and disappeared to become the great Artesian basin, weathering 30 million years ago released a lot of the silica into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of this silica became precious opal.

Australian Opal

Opal is predominantly found in Australia. 95% of it, to be exact, is found there, thus making opal the country’s national gemstone. The largest and most valuable opal, the Olympic Australis, was found in 1956 in the town of Coober Pedy, a major source of opal. Other sources of opal included Ethiopia, Nevada, Idaho, and even Mars, where NASA discovered opal deposits in 2008. Ethiopian opal comes from the Wollo and North Shewa Provinces. Wollo opal, also called “Welo” or “Wello” opal, has become the dominant Ethiopian opal in the gem trade. The Smithsonian Institute has he largest unpolished and polish black opals, both from Virgin Valley, Nevada. The unpolished opal is known as the “Roebling Opal,” which was found in 1917 and weighs 2,585 carats. The polish version is called the “Black Peacock” and weights 160 carats.

The major opal producing fields for black opal is Lightning Ridge in New South Wales, Australia, and to a much lesser degree Mintabie in South Australia. The most sought after black opal is red or multicolour on black, which is very difficult to find. Such stones are always cut on the fields and sold immediately. Boulder opal is opal that is formed in a brown ironstone nodule and is distinctive because it typically presents as a thin layer of opal over a dark brown base when cut. The opal can be quite superb. Opal from Lightning Ridge is often considered to be the best and brightest in the world.

Opal is one of the worlds most beautiful and precious gemstones and is one of six types of gemstones used throughout history, along with diamonds, rubies, sapphires, emeralds, and pearls. The word ‘opal’ is adapted from the Roman term opalus, but adapted from the Sanskrit word úpala. It is also the birthstone of October, but, since the 19th century, has been associated with bad luck and death thanks to the novel Anne of Geierstein, which uses opal as a plot device. Regardless, it remains likeable and wanted by gem collectors despite the superstition around it maintain the evil eye, as it is a gorgeous collectors item for enthusiasts of such items.

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Black Opal

Boulder Opal

Crystal Opal

Ethiopian Opal

Opal je nekristalni oblik mineralnog silicija. Opal je povezan s češćim kristalnim rođacima poput kvarca i ahata. Opal se razlikuje po tome što se formira od amorfnih kremena silike, a ne od prirodno klesanih kristala. Kemijski sastav opala je SiO2H2O, silicijev dioksid u kombinaciji s vodom (opal kamen može sadržavati do 30% vode.) Opal-ova Mohova tvrdoća mjeri se na 6,0 do 6,5 na skali sličnoj tvrdoći s kvarcom. Većina opala stara je više od 65 milijuna do 145 milijuna godina, a nalazi se u krednom sloju krede koji je bio u razdoblju kada su dinosauri lutali zemljom.

Opal ima tendenciju da se nalazi u blizini zemljine površine u područjima gdje su nekada tekla drevna geotermalna izvora. Minerali su se dizali ispod površine zemlje i polako su stoljećima polako postavljali zidove šupljina u podlozi. Više od 90% svjetskih kvalitetnih opala za drago kamenje potječe iz Južne Australije, iako ga možete pronaći u drugim dijelovima svijeta kao što su Etiopija, Brazil, Meksiko, Čehoslovačka i Nevada. Sav crni opal dolazi isključivo iz Australije.

Da bi se laički definirao opal, čvrsti dragulj mineraloid (koji ima mineralne karakteristike, ali nije jedan) učvršćen je iz kemijskog silicijevog dioksida, koji dolazi iz šupljina u propadajućoj vegetaciji, drvu i kostima. U naučnom načinu rada opal je poznat kao SiO2 · nH2O, miješajući silicijev dioksid s vodom. Za razliku od drugih dragulja, opal dolazi u mnogim sortama - bijeloj, plavoj, crvenoj, crnoj, pa čak i bezbojnoj. Njegov je jedinstven karakter to što prikazuje sve boje spektra koje nastaju uslijed smetnji i difrakcije svjetlosti koja prolazi kroz njega. Drugim riječima, svijetli dugin izgled opala, kakav se čini kad se vidi, kretat će se i dramatično mijenjati ovisno o kutu pod kojim se vidi kamen.

Opalne sorte

Postoje dvije glavne sorte opala - dragocjene i uobičajene. Dragocjeni opali pokazuju karakteristiku koja se naziva "igra u boji", a relativno su rijetke. Uobičajeni opal je dosadan i bezvrijedan i javlja se u izobilju u cijelom svijetu. Uobičajeni opal ne pokazuje igru boje. Kada se uobičajeni opal nađe u vezi s dragocjenim opalom, poznat je pod nazivom lonac. Otprilike 95% svih opala, koji se vade iz opalovih polja, su obične ili gipke, u osnovi jednobojne. Preostalih 5% ima neku boju, ali oko 95% je osrednje kvalitete. Stoga samo oko 0,25% uopće ima stvarnu vrijednost. Ostale vrste opala uključuju Vatreni opal, koji je proziran do proziran, plavi opal poznat pod nazivom peruanski Opal i Girasol opal, koji uglavnom dolazi iz Meksika, a koji pokazuje plavkast sjaj ili sjaj koji prati izvor svjetlosti oko kojeg nije igra boja.

Opal je sedimentaran

Opal je jedan od rijetkih dragulja koji je porijeklom sedimentalan. Opal i dalje sadrži 6 do 10 posto vode, ostatak tog drevnog mora. Zlatni panneri u Australiji pronašli su prvih nekoliko komada dragocjenog opala 1863. Veliki postotak stabilnog svjetskog komercijalnog opala potječe iz Australije, a postoje tri karakteristične regije odakle opal dolazi. To su Lightning Ridge (dom crnog opala), polja Južne Australije Coober Pedy, Mintabie, Lambina i Andamooka (glavni izvori svjetlosne baze opal) i polja Queenslanda, odakle potječe opal od gromade.

Opalescence

Najupečatljivija karakteristika opala je sposobnost refrakcije i odražavanja specifičnih valnih duljina boja. Zapravo je pojam opalescence skovan da bi opisao ovaj fenomen. Veličina i razmak amorfnih sfera silicija u kamenu refraktira određene valne duljine svjetlosti; a svaka sfera refraktira jednu jedinstvenu, čistu spektralnu boju sličnu kapljicama vode u dugi. Međusobna interakcija ovih čistih valnih duljina svjetla daje opalu njegovu jedinstvenu vizualnu privlačnost i čini ga jednim od najtraženijih dragulja na svijetu.

Povijest Opala

Opal sadrži čuda neba - pjenušave duge, vatromet i munje. Kao što se nebo opal boje mijenjaju i treptaju pokretom, kombinacija boja i uzoraka znači da je svaki opal jedinstven. Crni opal prvi je put otkriven u Australiji krajem 1800-ih. Prije otkrića, svijet je bio svjestan samo kristalnog opala koji se obično minirao u Istočnoj Europi. Mnoge kraljevske obitelji tijekom povijesti blago su se kladile u Europi i Africi. Najstariji zabilježeni opal pronašao je poznati arheolog Louis Leakey koji je u pećini u Keniji pronašao šest tisuća godina stare opalne artefakte! Rimski povjesničar Plinije s pravom je opisao opal kao kraljicu dragulja, jer je opal kombinacija ljepote svih ostalih dragulja: "U njima je mekša vatra od rubina, tamo je sjajna ljubičasta ametista i more zelena smaragda - sve zajedno blista u nevjerojatnom sjedinjenju. Neki se svojim sjajem boje boje slikara, drugi plamen gorućeg sumpora ili vatre koja je ubrzana uljem. "

Opals su bili popularni kod nekih od najvećih imena u povijesti, uključujući Kleopatru i Marca Anthonyja. Jedan od rimskih senatora Marca Anthonyja posjedovao je opalni kamen koji je toliko podsjećao na Marca iz Kleopatre da ga je morao imati. Kad mu je senator odbio prodati, poslao ga je u egzil. Francuski car Napoleon bio je uspješniji dajući Josephine lijepi opal s sjajnim crvenim bljeskovima nazvanim "Spaljivanje Troje", čineći ga svojom Helenom.

Opals su bili poznati i u književnosti. Shakespeare je nalikovao opalnoj igri boja da bi se igrala uma u najpoznatijoj upotrebi simbolike dragog kamenja u književnosti. U Dvanaestoj noći piše: "Sad te melanholiji Bog štiti, a krojač napravi odjeću promjenljivom taftom, jer ti je um opal." Činilo se da su nekoliko stoljeća nestali opali iz povijesti. Međutim, u moderno doba kraljica Viktorija ponovno je zanimala dragulj. Kraljica Viktorija obožavala je opals i često ih je davala kao vjenčane poklone. Ona i njezine kćeri stvorile su modni trend nošenja opala.

Kraljica Viktorija bila je jedna od prvih koja je cijenila opals iz uzbudljivog novog izvora: Australije. Priča o australskom opalu počinje prije više od 100 milijuna godina, kada su pustinje središnje Australije bile veliko unutarnje more, sa sedimentom natopljenim silicijem naslagnutim oko njegove obale. Nakon što se more povuklo i nestalo da bi postalo veliki arteški bazen, vremenski uvjeti prije 30 milijuna godina pustili su puno silicija u otopinu koja je punila pukotine u stijenama, slojeve u glini, pa čak i neke fosile. Neki od ovog silicija postali su dragocjeni opali.

Australijski Opal

Opal se pretežno nalazi u Australiji. Točno, 95% se nalazi tamo, što stvara opal nacionalnog dragog kamenja. Najveći i najvrijedniji opali, olimpijski Australis, pronađen je 1956. godine u gradu Coober Pedy, glavnom izvoru opala. Ostali izvori opala uključivali su Etiopiju, Nevadu, Idaho, pa čak i Mars, gdje je NASA otkrila naslage opala 2008. godine. Etiopski opal dolazi iz provincija Wollo i Sjeverna Shewa. Wollo opal, koji se naziva i "Welo" ili "Wello", postao je dominantni etiopski opal u trgovini draguljima. Smithsonian Institute ima najveći neoblikovani i polirani crni opali, oba iz Virgin Valley, Nevada. Nepolirani opal poznat je pod nazivom "Roebling Opal", a pronađen je 1917. godine i težak je 2585 karata. Poljska verzija naziva se "crni paun" i teži 160 karata.

Glavno polje za proizvodnju opal-a za crni opal je Lightning Ridge u Novom Južnom Walesu u Australiji, a u mnogo manjem broju Mintabie u Južnoj Australiji. Najtraženiji crni opali su crveni ili višebojni na crnom, što je vrlo teško pronaći. Takvo se kamenje uvijek sije na poljima i odmah prodaje. Opal od balvana je opal koji se formira u smeđem željeznom čvoru i karakterističan je po tome što se obično siječe u tankom sloju opala preko tamno smeđe baze. Opal može biti prilično vrhunski. Opal iz Lightning Ridgea često se smatra najboljim i najsvjetlijim na svijetu.

Opal je jedan od najljepših i najcjenjenijih dragulja na svijetu i jedan je od šest vrsta dragog kamenja koji se tijekom povijesti koristio, zajedno s dijamantima, rubinima, safirima, smaragdima i biserima. Riječ opal prilagođena je rimskom izrazu opalus, ali prilagođena sanskrtskoj riječi úpala. To je također kamen rođenja u listopadu, ali je od 19. stoljeća povezan s lošom srećom i smrću zahvaljujući romanu Anne od Geiersteina, koji koristi opal kao zavjeru. Bez obzira na to, kolekcionari dragulja ostaju simpatični i željeni usprkos sujeverju koje održava oko, jer je to prekrasan kolekcionarski predmet za ljubitelje takvih predmeta.