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Dull or waxy if corroded, porous or very impure.","Transparent,Translucent","White","Colourless, white, yellow, red, orange, green, brown, black, blue",[44,45,46,47,48,49,50,51,52],"colorless","white","yellow","red","orange","green","brown","black","blue",[45],"Yellow to green (uranyl)","None Observed","Irregular\u002FUneven,Splintery,Conchoidal","brittle","Isotropic","1.40","1.46",1.4,1.46,"Non-pleochroic","Opal-AG and Opal-AG are optically isotropic but may show anomalous birefringence due to strain. \r\nThe microcrystalline varieties show birefringence: opal-C is length-fast, opal-CT is length-slow, but almost isotropic.","See: Chauviré et. al. (2023) for dehydration crazing.","Gemstones","Altering volcanic tuffs, basalts. Silicious deep-water marine sediments. Opal-C, opal-CT and opal-AG formation is restricted to low pressure and low-temperature environments.","Although it is still (2007) regarded as a mineral species for historical reasons, opal is not a true mineral in the accepted sense of the word as it is variably composed of poorly crystalline material related to cristobalite and\u002For tridymite and\u002For com...","The origin of the name is uncertain. It may be from the Sanskrit \"upala\", meaning \"stone\" or \"precious stone\" or from opalus, the ancient Latin name for the gem (Pliny the Elder, 75-79). Pliny may have also referred to the gem as paederos, but a modern commentary by Kostov (2008)[[1]] questions if that name was actually applied to the opal in the modern sense.","2026-04-23 10:33:40",[72,77,80,83,86,90,93,96,100,104,108,111,115,118,122,126,129,132,136,139,143,147,151,155,159,163,166,170,173,176,180,184,188,192,196],{"id":73,"name":74,"entrytype":75,"csystem":11,"ima_formula":11,"mindat_formula":14,"hmin":11,"hmax":11,"dmeas":32,"dcalc":11,"primary_image_id":76},8081,"Alumocalcite",2,87579,{"id":78,"name":79,"entrytype":75,"csystem":11,"ima_formula":11,"mindat_formula":14,"hmin":11,"hmax":11,"dmeas":32,"dcalc":11,"primary_image_id":11},7996,"Amber Opal",{"id":81,"name":82,"entrytype":75,"csystem":11,"ima_formula":11,"mindat_formula":14,"hmin":11,"hmax":11,"dmeas":11,"dcalc":11,"primary_image_id":11},43544,"Andean 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Opal",[],[201,208,217,225,235,243,251,258],{"id":202,"name":203,"entrytype":75,"csystem":11,"ima_formula":11,"mindat_formula":204,"hmin":35,"hmax":205,"dmeas":206,"dcalc":32,"primary_image_id":207},960,"Chalcedony","SiO\u003Csub>2\u003C\u002Fsub>",7,"2.6",87926,{"id":209,"name":210,"entrytype":9,"csystem":211,"ima_formula":212,"mindat_formula":212,"hmin":75,"hmax":213,"dmeas":214,"dcalc":215,"primary_image_id":216},1052,"Cinnabar","Trigonal","HgS",2.5,"8.176","8.20",5743,{"id":218,"name":219,"entrytype":9,"csystem":220,"ima_formula":204,"mindat_formula":204,"hmin":221,"hmax":205,"dmeas":222,"dcalc":223,"primary_image_id":224},1155,"Cristobalite","Tetragonal",6,"2.32","2.33",6449,{"id":226,"name":227,"entrytype":9,"csystem":228,"ima_formula":229,"mindat_formula":230,"hmin":231,"hmax":231,"dmeas":232,"dcalc":233,"primary_image_id":234},1979,"Hydromagnesite","Monoclinic","Mg\u003Csub>5\u003C\u002Fsub>(CO\u003Csub>3\u003C\u002Fsub>)\u003Csub>4\u003C\u002Fsub>(OH)\u003Csub>2\u003C\u002Fsub> · 4H\u003Csub>2\u003C\u002Fsub>O","Mg\u003Csub>5\u003C\u002Fsub>(CO\u003Csub>3\u003C\u002Fsub>)\u003Csub>4\u003C\u002Fsub>(OH)\u003Csub>2\u003C\u002Fsub>·4H\u003Csub>2\u003C\u002Fsub>O",3.5,"2.24","2.25",11889,{"id":236,"name":237,"entrytype":9,"csystem":228,"ima_formula":238,"mindat_formula":239,"hmin":231,"hmax":231,"dmeas":240,"dcalc":241,"primary_image_id":242},2385,"Leucophosphite","KFe\u003Csup>3+\u003C\u002Fsup>\u003Csub>2\u003C\u002Fsub>(PO\u003Csub>4\u003C\u002Fsub>)\u003Csub>2\u003C\u002Fsub>(OH) · 2H\u003Csub>2\u003C\u002Fsub>O","KFe\u003Csup>3+\u003C\u002Fsup>\u003Csub>2\u003C\u002Fsub>(PO\u003Csub>4\u003C\u002Fsub>)\u003Csub>2\u003C\u002Fsub>(OH)·2H\u003Csub>2\u003C\u002Fsub>O","2.948","2.911",14428,{"id":244,"name":245,"entrytype":9,"csystem":246,"ima_formula":247,"mindat_formula":248,"hmin":213,"hmax":213,"dmeas":249,"dcalc":250,"primary_image_id":11},47023,"Magnesiovoltaite","Isometric","K\u003Csub>2\u003C\u002Fsub>Mg\u003Csub>5\u003C\u002Fsub>Fe\u003Csup>3+\u003C\u002Fsup>\u003Csub>3\u003C\u002Fsub>Al(SO\u003Csub>4\u003C\u002Fsub>)\u003Csub>12\u003C\u002Fsub> · 18H\u003Csub>2\u003C\u002Fsub>O","K\u003Csub>2\u003C\u002Fsub>Mg\u003Csub>5\u003C\u002Fsub>Fe\u003Csup>3+\u003C\u002Fsup>\u003Csub>3\u003C\u002Fsub>Al(SO\u003Csub>4\u003C\u002Fsub>)\u003Csub>12\u003C\u002Fsub>·18H\u003Csub>2\u003C\u002Fsub>O","2.51","2.506",{"id":252,"name":253,"entrytype":9,"csystem":254,"ima_formula":255,"mindat_formula":256,"hmin":75,"hmax":75,"dmeas":32,"dcalc":257,"primary_image_id":11},2697,"Metazellerite","Orthorhombic","Ca(UO\u003Csub>2\u003C\u002Fsub>)(CO\u003Csub>3\u003C\u002Fsub>)\u003Csub>2\u003C\u002Fsub> · 3H\u003Csub>2\u003C\u002Fsub>O","Ca(UO\u003Csub>2\u003C\u002Fsub>)(CO\u003Csub>3\u003C\u002Fsub>)\u003Csub>2\u003C\u002Fsub>·3H\u003Csub>2\u003C\u002Fsub>O","3.414",{"id":259,"name":260,"entrytype":9,"csystem":228,"ima_formula":261,"mindat_formula":262,"hmin":263,"hmax":263,"dmeas":264,"dcalc":265,"primary_image_id":266},3988,"Todorokite","(Na,Ca,K,Ba,Sr)\u003Csub>1-x\u003C\u002Fsub>(Mn,Mg,Al)\u003Csub>6\u003C\u002Fsub>O\u003Csub>12\u003C\u002Fsub> · 3-4H\u003Csub>2\u003C\u002Fsub>O","(Na,Ca,K,Ba,Sr)\u003Csub>1-x\u003C\u002Fsub>(Mn,Mg,Al)\u003Csub>6\u003C\u002Fsub>O\u003Csub>12\u003C\u002Fsub>·3-4H\u003Csub>2\u003C\u002Fsub>O",1.5,"3.67","3.65",24311,[],[],2965,[271,274,279,283,288,293,298,302,306,310,313,317,321,326,331,336,340,344,348,352,356,361,364,369,373,378,383,388,392,397,401,406],{"id":272,"year":11,"html":273,"doi":11},16925025,"Pineau, M., Chauviré, B., Rondeau, B. (2023): Near-infrared signature of hydrothermal opal: a case study of Icelandic silica sinters. European Journal of Mineralogy, 35, 949–967.",{"id":275,"year":276,"html":277,"doi":278},2522392,1964,"JONES, J. B., SANDERS, J. V., SEGNIT, E. R. (1964) Structure of Opal. \u003Ci>Nature\u003C\u002Fi>, 204 (4962). 990-991 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1038\u002F204990a0'>doi:10.1038\u002F204990a0\u003C\u002Fa>","10.1038\u002F204990a0",{"id":280,"year":276,"html":281,"doi":282},2522986,"SANDERS, J. V. (1964) Colour of Precious Opal. \u003Ci>Nature\u003C\u002Fi>, 204 (4964). 1151-1153 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1038\u002F2041151a0'>doi:10.1038\u002F2041151a0\u003C\u002Fa>","10.1038\u002F2041151a0",{"id":284,"year":285,"html":286,"doi":287},2540609,1966,"JONES, J. B., BIDDLE, J., SEGNIT, E. R. (1966) Opal Genesis. \u003Ci>Nature\u003C\u002Fi>, 210 (5043). 1353-1354 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1038\u002F2101353a0'>doi:10.1038\u002F2101353a0\u003C\u002Fa>","10.1038\u002F2101353a0",{"id":289,"year":290,"html":291,"doi":292},183471,1968,"Sanders, J. V. (1968) Diffraction of light by opals. \u003Ci>Acta Crystallographica Section A\u003C\u002Fi>,  24 (4) 427-434 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1107\u002Fs0567739468000860'>doi:10.1107\u002Fs0567739468000860\u003C\u002Fa>","10.1107\u002Fs0567739468000860",{"id":294,"year":295,"html":296,"doi":297},565312,1971,"Jones, J. B., Segnit, E. R. (1971) The nature of opal I. nomenclature and constituent phases. \u003Ci>Journal of the Geological Society of Australia\u003C\u002Fi>,  18 (1) 57-68 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1080\u002F00167617108728743'>doi:10.1080\u002F00167617108728743\u003C\u002Fa>","10.1080\u002F00167617108728743",{"id":299,"year":300,"html":301,"doi":11},16119003,1981,"Kalokerinos, A. (1981) Opal. Edelstein der tausend Farben. Ein Buch für Sammler und Liebhaber. Stuttgart.",{"id":303,"year":304,"html":305,"doi":11},16984013,1983,"Komotauer, Simon K. (1983) Mineralarten im Bild: Opal, SiO2 · nH2O [Minerals in the picture: Opal, SiO2 · nH2O]. \u003Ci>Mineralien Magazin\u003C\u002Fi>,  7 (2) 55-59",{"id":307,"year":308,"html":309,"doi":11},16119008,1994,"Li, D., Bancroft, G.M., Kasrai, M., Fleet, M.E., Secco, R.A., Feng, X.H., Tan, K.H., Yang, B.X. (1994) X-ray absorption spectroscopy of silicon dioxide (SiO2) polymorphs: the structural characterization of opal. American Mineralogist: 79: 622-632.",{"id":311,"year":308,"html":312,"doi":11},16121337,"Graetsch, H. (1994) Structural characteristics of opaline and microcrystalline silica minerals. in: Heaney, P.J., Gibbs, G.V., editors. Reviews in Mineralogy Volume 29 Silica - Physical behaviour, geochemistry and materials applications. Mineralogical Society of America, 209-232.",{"id":314,"year":308,"html":315,"doi":316},3235954,"Elzea, J.M., Odom, I.E., Miles, W.J. (1994) Distinguishing well ordered opal-CT and opal-C from high temperature cristobalite by x-ray diffraction. \u003Ci>Analytica Chimica Acta\u003C\u002Fi>, 286 (1). 107-116 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1016\u002F0003-2670(94)80182-7'>doi:10.1016\u002F0003-2670(94)80182-7\u003C\u002Fa>","10.1016\u002F0003-2670(94)80182-7",{"id":318,"year":319,"html":320,"doi":11},16119009,1996,"Weise, C., publisher (1996) Opal - extraLapis Nr.10. Christian Weise Verlag, München.",{"id":322,"year":323,"html":324,"doi":325},13253764,1998,"(1998) Opal, cristobalite, and tridymite: Noncrystallinity versus crystallinity, nomenclature of the silica minerals and bibliography. \u003Ci>Powder Diffraction\u003C\u002Fi>, 13 (1) 2-19 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1017\u002Fs0885715600009696'>doi:10.1017\u002Fs0885715600009696\u003C\u002Fa>","10.1017\u002Fs0885715600009696",{"id":327,"year":328,"html":329,"doi":330},641384,2003,"Bustillo, M (2003) Green opals in hydrothermalized basalts (Tenerife Island, Spain): alteration and aging of silica pseudoglass. \u003Ci>Journal of Non-Crystalline Solids\u003C\u002Fi>,  323 (1) 27-33 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1016\u002Fs0022-3093(03)00288-6'>doi:10.1016\u002Fs0022-3093(03)00288-6\u003C\u002Fa>","10.1016\u002Fs0022-3093(03)00288-6",{"id":332,"year":333,"html":334,"doi":335},7868655,2007,"JONES, BRIAN, RENAUT, ROBIN W. (2007) Microstructural changes accompanying the opal-A to opal-CT transition: new evidence from the siliceous sinters of Geysir, Haukadalur, Iceland. \u003Ci>Sedimentology\u003C\u002Fi>, 54 (4). 921-948 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1111\u002Fj.1365-3091.2007.00866.x'>doi:10.1111\u002Fj.1365-3091.2007.00866.x\u003C\u002Fa>","10.1111\u002Fj.1365-3091.2007.00866.x",{"id":337,"year":338,"html":339,"doi":11},16119011,2008,"Kostov, Rusian I. (2008) Orphic Lithica As A Source Of Late Antiquity Mineralogical Knowledge. \u003Ci>Annual Of The University Of Mining And Geology “ST. Ivan Rilski”\u003C\u002Fi>,  51 (1) 109-115",{"id":341,"year":338,"html":342,"doi":343},1104439,"Day, R., Jones, B. (2008) Variations in Water Content in Opal-A and Opal-CT from Geyser Discharge Aprons. \u003Ci>Journal of Sedimentary Research\u003C\u002Fi>,  78 (4) 301-315 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.2110\u002Fjsr.2008.030'>doi:10.2110\u002Fjsr.2008.030\u003C\u002Fa>","10.2110\u002Fjsr.2008.030",{"id":345,"year":338,"html":346,"doi":347},395937,"Gaillou, E., Fritsch, E., Aguilar-Reyes, B., Rondeau, B., Post, J., Barreau, A., Ostroumov, M. (2008) Common gem opal: An investigation of micro- to nano-structure. \u003Ci>American Mineralogist\u003C\u002Fi>,  93 (11) 1865-1873 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.2138\u002Fam.2008.2518'>doi:10.2138\u002Fam.2008.2518\u003C\u002Fa>","10.2138\u002Fam.2008.2518",{"id":349,"year":350,"html":351,"doi":11},16119012,2010,"Adamo, I., Ghisoli, C. & Caucia, F. (2010) A contribution to the study of FTIR spectra of opals. Neues Jahrbuch für Mineralogie - Abhandlungen: 187: 63-68.",{"id":353,"year":354,"html":355,"doi":11},16119013,2013,"Caucia, F., Ghisoli, C., Marinoni, L., Bordoni, V. (2013) Opal, a beautiful gem between myth and reality. Neues Jahrbuch für Mineralogie - Abhandlungen: 190: 1-9.",{"id":357,"year":358,"html":359,"doi":360},129388,2015,"Eckert, Jürgen, Gourdon, Olivier, Jacob, Dorrit E., Meral, Cagla, Monteiro, Paulo J.M., Vogel, Sven C., Wirth, Richard, Wenk, Hans-Rudolf (2015) Ordering of water in opals with different microstructures. \u003Ci>European Journal of Mineralogy\u003C\u002Fi>,  27 (2) 203-213 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1127\u002Fejm\u002F2015\u002F0027-2428'>doi:10.1127\u002Fejm\u002F2015\u002F0027-2428\u003C\u002Fa>","10.1127\u002Fejm\u002F2015\u002F0027-2428",{"id":362,"year":358,"html":363,"doi":11},17515230,"Gaillou, Eloïse (2015) An Overview of Gem Opals: From the Geology to Color and Microstructure. \u003Ci>13th Sinkankas Symposium\u003C\u002Fi>,  13. Pala International. 10-20",{"id":365,"year":366,"html":367,"doi":368},298665,2016,"Othmane, Guillaume, Allard, Thierry, Vercouter, Thomas, Morin, Guillaume, Fayek, Mostafa, Calas, Georges (2016) Luminescence of uranium-bearing opals: Origin and use as a pH record. \u003Ci>Chemical Geology\u003C\u002Fi>,  423. 1-6 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1016\u002Fj.chemgeo.2015.12.010'>doi:10.1016\u002Fj.chemgeo.2015.12.010\u003C\u002Fa>","10.1016\u002Fj.chemgeo.2015.12.010",{"id":370,"year":366,"html":371,"doi":372},2437703,"Sodo, A., Casanova Municchia, A., Barucca, S., Bellatreccia, F., Della Ventura, G., Butini, F., Ricci, M. A. (2016) Raman, FT-IR and XRD investigation of natural opals. \u003Ci>Journal of Raman Spectroscopy\u003C\u002Fi>, 47 (12). 1444-1451 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.1002\u002Fjrs.4972'>doi:10.1002\u002Fjrs.4972\u003C\u002Fa>","10.1002\u002Fjrs.4972",{"id":374,"year":375,"html":376,"doi":377},398381,2017,"Schindler, Michael, Fayek, Mostafa, Courchesne, Britanney, Kyser, Kurt, Hawthorne, Frank C. (2017) Uranium-bearing opals: Products of U-mobilization, diffusion, and transformation processes. \u003Ci>American Mineralogist\u003C\u002Fi>,  102 (6) 1154-1164 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.2138\u002Fam-2017-5700'>doi:10.2138\u002Fam-2017-5700\u003C\u002Fa>","10.2138\u002Fam-2017-5700",{"id":379,"year":380,"html":381,"doi":382},13422495,2021,"Curtis, Neville J., Gascooke, Jason R., Pring, Allan (2021) Silicon-Oxygen Region Infrared and Raman Analysis of Opals: The Effect of Sample Preparation and Measurement Type. \u003Ci>Minerals\u003C\u002Fi>, 11 (2) 173 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.3390\u002Fmin11020173'>doi:10.3390\u002Fmin11020173\u003C\u002Fa> \u003Ca target='_blank' href='https:\u002F\u002Fwww.mdpi.com\u002F2075-163X\u002F11\u002F2\u002F173\u002Fpdf?version=1613739472' class='refpdflink'>\u003C\u002Fa>","10.3390\u002Fmin11020173",{"id":384,"year":385,"html":386,"doi":387},13420893,2022,"Curtis, Neville J., Gascooke, Jason R., Johnston, Martin R., Pring, Allan (2022) 29Si Solid-State NMR Analysis of Opal-AG, Opal-AN and Opal-CT: Single Pulse Spectroscopy and Spin-Lattice T1 Relaxometry. \u003Ci>Minerals\u003C\u002Fi>, 12 (3) 323 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.3390\u002Fmin12030323'>doi:10.3390\u002Fmin12030323\u003C\u002Fa> \u003Ca target='_blank' href='https:\u002F\u002Fwww.mdpi.com\u002F2075-163X\u002F12\u002F3\u002F323\u002Fpdf?version=1646634113' class='refpdflink'>\u003C\u002Fa>","10.3390\u002Fmin12030323",{"id":389,"year":385,"html":390,"doi":391},16112332,"Lee, Seungyeol, Xu, Huifang, Xu, Hongwu (2022) Reexamination of the structure of opal-A: A combined study of synchrotron X-ray diffraction and pair distribution function analysis. \u003Ci>American Mineralogist\u003C\u002Fi>,  107 (7) 1353-1360 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.2138\u002Fam-2022-8017'>doi:10.2138\u002Fam-2022-8017\u003C\u002Fa>","10.2138\u002Fam-2022-8017",{"id":393,"year":394,"html":395,"doi":396},15707069,2023,"Lv, Huiyu, Guo, Ying (2023) Genesis of the Body Color of Brazilian Gem-Quality Yellow-Green Opal. \u003Ci>Crystals\u003C\u002Fi>, 13 (2) 316 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.3390\u002Fcryst13020316'>doi:10.3390\u002Fcryst13020316\u003C\u002Fa>","10.3390\u002Fcryst13020316",{"id":398,"year":394,"html":399,"doi":400},15738507,"Chauviré, Boris, Mollé, Valentin, Guichard, Florine, Rondeau, Benjamin, Thomas, Paul Stephen, Fritsch, Emmanuel (2023) Cracking of Gem Opals. \u003Ci>Minerals\u003C\u002Fi>, 13 (3) 356 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.3390\u002Fmin13030356'>doi:10.3390\u002Fmin13030356\u003C\u002Fa> \u003Ca target='_blank' href='https:\u002F\u002Fwww.mdpi.com\u002F2075-163X\u002F13\u002F3\u002F356\u002Fpdf?version=1677826705' class='refpdflink'>\u003C\u002Fa>","10.3390\u002Fmin13030356",{"id":402,"year":403,"html":404,"doi":405},17612836,2024,"Gouzy, Simon, Rondeau, Benjamin, Vinogradoff, Vassilissa, Chauviré, Boris, Coulet, Marie-Vanessa, Grauby, Olivier, Terrisse, Hélène, Carter, John (2024) Opal Synthesis: Toward Geologically Relevant Conditions. \u003Ci>Minerals\u003C\u002Fi>,  14 (10).  \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.3390\u002Fmin14100969'>doi:10.3390\u002Fmin14100969\u003C\u002Fa>","10.3390\u002Fmin14100969",{"id":407,"year":408,"html":409,"doi":410},18692840,2025,"Gouzy, S.; Phan, V.T.H.; Bejach, L.; Vinogradoff, V.; Rondeau, B.; Chauviré, B.; Beck, P.; Flandinet, L.; Franz, G.; Khomenko, V.; et al. (2025) Preservation of biosignatures in opal probed by infrared nanospectroscopy. \u003Ci>Geochemical Perspectives Letters\u003C\u002Fi>,  35. 42-48 \u003Ca target='_blank' href='https:\u002F\u002Fdoi.org\u002F10.7185\u002Fgeochemlet.2522'>doi:10.7185\u002Fgeochemlet.2522\u003C\u002Fa>","10.7185\u002Fgeochemlet.2522",[412,421,431,440,450,460,467,477,486,495,505,513,522,531,537,546,555,564,572,581,590,599,607,611,618,624,629,634,638,642,647,652,656],{"id":413,"source_url":414,"license_code":415,"credit_html":416,"title":417,"description":418,"author":419,"original_width":366,"original_height":420},18161,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=7448299","CC BY-SA 2.5","JJ Harrison (https:\u002F\u002Fwww.jjharrison.com.au\u002F), via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=7448299\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal from Yowah, Queensland, Australia 2.jpg","\u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FOpal\" class=\"extiw\" title=\"en:Opal\">Opal\u003C\u002Fa> from Yowah, Queensland, Australia. Length: about 20mm.","JJ Harrison (https:\u002F\u002Fwww.jjharrison.com.au\u002F)",1344,{"id":422,"source_url":423,"license_code":424,"credit_html":425,"title":426,"description":427,"author":428,"original_width":429,"original_height":430},18165,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=132610877","CC BY-SA 4.0","Eric Polk, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=132610877\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal NHMLA.png","Sample of Opal collected from Queensland, Australia.  On display at the Natural History Museum of Los Angeles County, Los Angeles, California, USA.","Eric Polk",2621,1503,{"id":432,"source_url":433,"license_code":424,"credit_html":434,"title":435,"description":436,"author":437,"original_width":438,"original_height":439},18167,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=165063526","Bobjgalindo, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=165063526\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal from Opal Butte, Oregon.jpg","Opal from Opal Butte, northern Oregon","Bobjgalindo",3024,4032,{"id":441,"source_url":442,"license_code":443,"credit_html":444,"title":445,"description":446,"author":447,"original_width":448,"original_height":449},37677,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=167126918","CC BY 4.0","Animalculum, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=167126918\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal Pineapple, Musee de Mineralogie, Paris, 2025.jpg","Opal \"Pineapple\" from White Cliffs, NSW, Australia in Musee de Mineralogie, Paris","Animalculum",2086,2781,{"id":451,"source_url":452,"license_code":453,"credit_html":454,"title":455,"description":456,"author":457,"original_width":458,"original_height":459},34449,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=180371023","CC0 1.0","RegionVisitor90, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=180371023\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal and Gemstone Studio, Hahndorf 20251219-122453.jpg","Green aventurine","RegionVisitor90",2158,2339,{"id":461,"source_url":462,"license_code":453,"credit_html":463,"title":464,"description":465,"author":466,"original_width":439,"original_height":438},46745,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=127851396","Romaine, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=127851396\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Mexico-opaal (3).jpg","opal from Mexico","Romaine",{"id":468,"source_url":469,"license_code":470,"credit_html":471,"title":472,"description":473,"author":474,"original_width":475,"original_height":476},59845,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=703240","CC BY-SA 3.0","No machine-readable author provided. Kluka assumed (based on copyright claims)., via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=703240\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Hialit, opal szklany Czechy ok. Podboran.jpg","hialit, opal szklany, pochodzenie Czechy, okolice Podboran; autor zdjęcia Piotr Gut 2006","No machine-readable author provided. Kluka assumed (based on copyright claims).",640,480,{"id":478,"source_url":479,"license_code":424,"credit_html":480,"title":481,"description":482,"author":483,"original_width":484,"original_height":485},60190,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=82981876","Mai Seppel, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=82981876\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Estonian Museum of Natural History Specimen No 201917 photo (g27 g27-249 1 jpg).jpg","\"opaal\", \"hüdrofaan\". More info \u003Ca rel=\"nofollow\" class=\"external text\" href=\"http:\u002F\u002Fgeocollections.info\u002Ffile\u002F91616\">about this file\u003C\u002Fa> and \u003Ca rel=\"nofollow\" class=\"external text\" href=\"http:\u002F\u002Fgeocollections.info\u002Fspecimen\u002F201917\">about this specimen\u003C\u002Fa> at \u003Ca rel=\"nofollow\" class=\"external text\" href=\"http:\u002F\u002Fgeocollections.info\u002F\">geocollections.info\u003C\u002Fa>","Mai Seppel",4409,3169,{"id":487,"source_url":488,"license_code":424,"credit_html":489,"title":490,"description":491,"author":492,"original_width":493,"original_height":494},64251,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=108328020","Secretlondon, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=108328020\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Lemon fruits sweets unwrapped aug 21.jpg","Opal Fruits are a previous name of Starburst in the UK. As a marketing thing they brought back Opal fruits in a limited edition. Lemon chew unwrapped but with wrapper","Secretlondon",1692,1799,{"id":496,"source_url":497,"license_code":498,"credit_html":499,"title":500,"description":501,"author":502,"original_width":503,"original_height":504},65824,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=84625620","CC BY 2.0","James St. John, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=84625620\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Dendritic opal (29816456982).jpg","\u003Cp>Dendritic opal (public display, Nebraska State Museum of Natural History, Lincoln, Nebraska, USA)\n\u003C\u002Fp>\u003Cp>A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties.  At its simplest, a mineral is a naturally-occurring solid chemical.  Currently, there are over 5400 named and described minerals - about 200 of them are common and about 20 of them are very common.  Mineral classification is based on anion chemistry.  Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.\n\u003C\u002Fp>\u003Cp>The silicates are the most abundant and chemically complex group of minerals.  All silicates have silica as the basis for their chemistry.  \"Silica\" refers to SiO2 chemistry.  The fundamental molecular unit of silica is one small silicon atom surrounded by four large oxygen atoms in the shape of a triangular pyramid - this is the silica tetrahedron - SiO4.  Each oxygen atom is shared by two silicon atoms, so only half of the four oxygens \"belong\" to each silicon.  The resulting formula for silica is thus SiO2, not SiO4.\n\u003C\u002Fp>\u003Cp>Opal is hydrous silica (SiO2·nH2O).  Technically, opal is not a mineral because it lacks a crystalline structure.  Opal is supposed to be called a mineraloid.  Opal is made up of extremely tiny spheres (colloids - <a href=\"\u003Ca rel=\"nofollow\" class=\"external free\" href=\"https:\u002F\u002Fwww.uwgb.edu\u002Fdutchs\u002Facstalks\u002Facscolor\u002FOPALSPHR.jpg\">https:\u002F\u002Fwww.uwgb.edu\u002Fdutchs\u002Facstalks\u002Facscolor\u002FOPALSPHR.jpg\u003C\u002Fa>\" rel=\"noreferrer nofollow\">www.uwgb.edu\u002Fdutchs\u002Facstalks\u002Facscolor\u002FOPALSPHR.jpg<\u002Fa>) that can be seen with a scanning electron microscope (SEM).\n\u003C\u002Fp>\u003Cp>Gem-quality opal, or precious opal, has a wonderful rainbow play of colors (opalescence).  This play of color is the result of light being diffracted by planes of voids between large areas of regularly packed, same-sized opal colloids.  Different opalescent colors are produced by colloids of differing sizes.  If individual colloids are larger than 140 x 10-6 millimeters in size, purple & blue & green colors are produced.  Once colloids get as large as about 240 x 10-6 millimeters, red color is seen (Carr et al., 1979).\n\u003C\u002Fp>\u003Cp>Not all opals have the famous play of colors, however.  Common opal has a wax-like luster & is often milky whitish with no visible color play at all.  Opal is moderately hard (H = 5 to 6), has a white streak, and has conchoidal fracture.\n\u003C\u002Fp>\u003Cp>Several groups of organisms make skeletons of opaline silica, for example hexactinellid sponges, diatoms, radiolarians, silicoflagellates, and ebridians.  Some organisms incorporate opal into their tissues, for example horsetails\u002Fscouring rushes and sawgrass.  Sometimes, fossils are preserved in opal or precious opal.\n\u003C\u002Fp>\u003Cp>\"Dendritic opal\" is a rockhound\u002Fcollectors term for common opal that has dark-colored, complexly branching \"inclusions\".  Many of these are likely manganese oxide, which frequently forms \"manganese dendrites\" along bedding planes and joint surfaces in many rocks.\n\u003C\u002Fp>\u003Cp>Locality: unrecorded\u002Fundisclosed\n\u003C\u002Fp>\n\u003Chr>\n\u003Cp>Photo gallery of opal:\n<a href=\"\u003Ca rel=\"nofollow\" class=\"external free\" href=\"http:\u002F\u002Fwww.mindat.org\u002Fgallery.php?min=3004\">http:\u002F\u002Fwww.mindat.org\u002Fgallery.php?min=3004\u003C\u002Fa>\" rel=\"noreferrer nofollow\">www.mindat.org\u002Fgallery.php?min=3004<\u002Fa>\n\u003C\u002Fp>\n\u003Chr>\n\u003Cp>References cited:\n\u003C\u002Fp>\nCarr et al. (1979) - Andamooka opal fields: the geology of the precious stones field and the results of the subsidised mining program.  Geological Survey of South Australia Department of Mines and Energy Report of Investigations 51.  68 pp.","James St. John",2590,1119,{"id":506,"source_url":507,"license_code":508,"credit_html":509,"title":510,"description":11,"author":11,"original_width":511,"original_height":512},9752,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=577741","Public domain","Unknown author, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=577741\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opal banded.jpg",985,623,{"id":514,"source_url":515,"license_code":443,"credit_html":516,"title":517,"description":518,"author":519,"original_width":520,"original_height":521},18175,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=158751481","Bim24, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=158751481\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Opalite is a man-made glass that is often used as a gemstone.jpg","Opalite is a man-made glass that is often used as a gemstone. It is designed to imitate opal, but unlike natural opal, it doesn't have the same play of color (the shifting of colors seen in opal). Opalite typically has a milky or translucent appearance, and it may show iridescent or pearlescent effects depending on how the light hits it. While it's not a true mineral, it is valued for its aesthetic appeal and is often used in jewelry and decorative items. The term \"opalite\" can sometimes refer to other materials, but it is most commonly associated with this synthetic glass.","Bim24",921,928,{"id":523,"source_url":524,"license_code":508,"credit_html":525,"title":526,"description":527,"author":528,"original_width":529,"original_height":530},20549,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=12690935","Modris Baum, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=12690935\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Birnessite, Rancieite, Aegirine, Opal, Microcline - Demix-Varennes quarry, Saint-Amable sill, Quebec, Canada.jpg","\u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FBirnessite\" class=\"extiw\" title=\"en:Birnessite\">Birnessite\u003C\u002Fa>, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FRancieite\" class=\"extiw\" title=\"en:Rancieite\">Rancieite\u003C\u002Fa>, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FAegirine\" class=\"extiw\" title=\"en:Aegirine\">Aegirine\u003C\u002Fa>, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FOpal\" class=\"extiw\" title=\"en:Opal\">Opal\u003C\u002Fa>, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FMicrocline\" class=\"extiw\" title=\"en:Microcline\">Microcline\u003C\u002Fa> (picture width: 4.7 x 6.8 mm)\n\u003Cdl>\u003Cdd>\u003Cdl>\u003Cdd>Locality: Demix-Varennes quarry, Saint-Amable sill, Varennes & St-Amable, Lajemmerais RCM, Montérégie, Québec, Canada\u003C\u002Fdd>\n\u003Cdd>\u003Ci>Original description:\u003C\u002Fi> Pseudomorph of birnessite\u002Franciéite probably after serandite. (Thanks to Laszlo Horvath for information regarding the ranciéite.) The microcline is white. The olive green \"urchins\" are aegirine - very typical for STA. There are a few small colorless droplets of bright green fluorescent opal on the microcline.\u003C\u002Fdd>\u003C\u002Fdl>\u003C\u002Fdd>\u003C\u002Fdl>","Modris Baum",711,1024,{"id":532,"source_url":533,"license_code":424,"credit_html":534,"title":7,"description":11,"author":11,"original_width":535,"original_height":536},30171,"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61187","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61187\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",1000,750,{"id":538,"source_url":539,"license_code":424,"credit_html":540,"title":541,"description":542,"author":543,"original_width":544,"original_height":545},33139,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=42244959","Eunostos, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=42244959\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Anorthite labradorite et opale.JPG","Anorthite labradorite (à gauche) et opale (à droite). L'anorthite labradorite vient du Labrador, au Canada, et fait partie de l'ancienne collection Vésignié. L'opale vient de Coober Pedy, en Australie méridionale, et est un don de M. Schubnel. Galerie de Minéralogie et de Géologie du Muséum national d'histoire naturelle, à Paris, en France.","Eunostos",1632,1224,{"id":547,"source_url":548,"license_code":424,"credit_html":549,"title":550,"description":551,"author":552,"original_width":553,"original_height":554},50459,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=46276364","DimaVoroba, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=46276364\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Kopal.jpg","Копал с инклюзами","DimaVoroba",721,416,{"id":556,"source_url":557,"license_code":470,"credit_html":558,"title":559,"description":560,"author":561,"original_width":562,"original_height":563},59858,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10174296","Robert M. Lavinsky, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10174296\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Beryl-Opal-290188.jpg","\u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FBeryl\" class=\"extiw\" title=\"en:Beryl\">Beryl\u003C\u002Fa> (Var.: \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FAquamarine\" class=\"extiw\" title=\"en:Aquamarine\">Aquamarine\u003C\u002Fa>), \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FOpal\" class=\"extiw\" title=\"en:Opal\">Opal\u003C\u002Fa> (Var.: \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FOpal\" class=\"extiw\" title=\"en:Opal\">Opal-AN\u003C\u002Fa>)\n\u003Cdl>\u003Cdd>\u003Cdl>\u003Cdd>Locality: Erongo Mountain, Usakos and Omaruru Districts, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FErongo_Region\" class=\"extiw\" title=\"en:Erongo Region\">Erongo Region\u003C\u002Fa>, Namibia (\u003Ca rel=\"nofollow\" class=\"external text\" href=\"http:\u002F\u002Fwww.mindat.org\u002Floc-21818.html\">Locality at mindat.org\u003C\u002Fa>)\u003C\u002Fdd>\n\u003Cdd>Size: 3.8 x 2.6 x 2.5 cm.\u003C\u002Fdd>\n\u003Cdd>A gemmy, highly lustrous Aquamarine with great color. The upper 2 cm is gem-clear and architecturally indented. This form is totally a matter of growth, and is intricate in person. At 41 g, this is a large, impressive, and quality gem Erongo aquamarine. Ex. Charlie Key.\u003C\u002Fdd>\u003C\u002Fdl>\u003C\u002Fdd>\u003C\u002Fdl>","Robert M. Lavinsky",465,354,{"id":565,"source_url":566,"license_code":470,"credit_html":567,"title":568,"description":569,"author":561,"original_width":570,"original_height":571},62866,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10450855","Robert M. Lavinsky, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10450855\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Kleinite-Opal-klein11c.jpg","\u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FKleinite\" class=\"extiw\" title=\"en:Kleinite\">Kleinite\u003C\u002Fa>, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FOpal\" class=\"extiw\" title=\"en:Opal\">Opal\u003C\u002Fa>\n\u003Cdl>\u003Cdd>\u003Cdl>\u003Cdd>Locality: McDermitt Mine (Cordero Mine; Old Cordero Mine), Opalite District, Humboldt County, \u003Ca href=\"https:\u002F\u002Fen.wikipedia.org\u002Fwiki\u002FNevada\" class=\"extiw\" title=\"en:Nevada\">Nevada\u003C\u002Fa>, USA (\u003Ca rel=\"nofollow\" class=\"external text\" href=\"http:\u002F\u002Fwww.mindat.org\u002Floc-4206.html\">Locality at mindat.org\u003C\u002Fa>)\u003C\u002Fdd>\n\u003Cdd>Size: miniature, 5.4 x 5.4 x 4.4 cm\n\u003Cdl>\u003Cdt>Kleinite with Hyalite Opal\u003C\u002Fdt>\u003C\u002Fdl>\u003C\u002Fdd>\n\u003Cdd>A rich, representative sample with many crystals enmeshed in pockets of the matrix, capped with a snowy, bright white layer of hyalite opal like frosting on a cake\u003C\u002Fdd>\u003C\u002Fdl>\u003C\u002Fdd>\u003C\u002Fdl>",1549,1800,{"id":573,"source_url":574,"license_code":470,"credit_html":575,"title":576,"description":577,"author":578,"original_width":579,"original_height":580},66513,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=704485","Simon Eugster --Simon 17:42, 14 April 2006 (UTC), via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=704485\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Matrix-Opal.jpg","Matrix-Opal","Simon Eugster --Simon 17:42, 14 April 2006 (UTC)",1078,813,{"id":582,"source_url":583,"license_code":470,"credit_html":584,"title":585,"description":586,"author":587,"original_width":588,"original_height":589},66514,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10846029","CRPeters, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=10846029\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","OpalStriations.jpg","A rock with Matrix opal striations throughout","CRPeters",3072,2304,{"id":591,"source_url":592,"license_code":470,"credit_html":593,"title":594,"description":595,"author":596,"original_width":597,"original_height":598},66516,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=30563197","Dpulitzer, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=30563197\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Andamooka matrix opal.jpg","31 ct. cabochon of treated matrix opal from Andamooka, South Australia.","Dpulitzer",937,1405,{"id":600,"source_url":601,"license_code":424,"credit_html":602,"title":603,"description":604,"author":605,"original_width":439,"original_height":606},86790,"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=137851695","Onceuponashell, via \u003Ca href=\"https:\u002F\u002Fcommons.wikimedia.org\u002F?curid=137851695\" rel=\"noopener\">Wikimedia Commons\u003C\u002Fa>","Gypsum in the Yowah Opal Field.jpg","Cross section of naturally  formed gypsum in the Yowah Opal Field.","Onceuponashell",2268,{"id":76,"source_url":608,"license_code":424,"credit_html":609,"title":7,"description":11,"author":11,"original_width":535,"original_height":610},"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61943","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61943\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",666,{"id":612,"source_url":613,"license_code":424,"credit_html":614,"title":615,"description":11,"author":11,"original_width":616,"original_height":617},88246,"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=8cf8d7934ebc498884f7e4689e652cc4","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=8cf8d7934ebc498884f7e4689e652cc4\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana","Opal; SiO2; Tectosilicați",1200,1060,{"id":619,"source_url":620,"license_code":424,"credit_html":621,"title":622,"description":11,"author":11,"original_width":623,"original_height":616},88247,"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=4fb71ce5d96b4073b233cb59e5950ef1","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=4fb71ce5d96b4073b233cb59e5950ef1\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana","Opal; SiO2; tectosilicați",1075,{"id":625,"source_url":626,"license_code":424,"credit_html":627,"title":628,"description":11,"author":11,"original_width":616,"original_height":521},88248,"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=1fb590b13a644181bbeffc844a7c3eb6","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=1fb590b13a644181bbeffc844a7c3eb6\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana","Opal; SiO2 nH2O; Tectosilicați",{"id":630,"source_url":631,"license_code":424,"credit_html":632,"title":628,"description":11,"author":11,"original_width":616,"original_height":633},88249,"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=952ae0d9f123402f90dcbc1c60524e14","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=952ae0d9f123402f90dcbc1c60524e14\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana",1088,{"id":121,"source_url":635,"license_code":424,"credit_html":636,"title":628,"description":11,"author":11,"original_width":616,"original_height":637},"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=f1aa4892d041474ab34fb4adb75f6c96","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=f1aa4892d041474ab34fb4adb75f6c96\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana",1030,{"id":639,"source_url":640,"license_code":424,"credit_html":641,"title":7,"description":11,"author":11,"original_width":535,"original_height":610},88439,"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61941","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61941\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",{"id":643,"source_url":644,"license_code":424,"credit_html":645,"title":7,"description":11,"author":11,"original_width":535,"original_height":646},88460,"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F91616","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F91616\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",718,{"id":648,"source_url":649,"license_code":424,"credit_html":650,"title":628,"description":11,"author":11,"original_width":651,"original_height":616},88505,"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=3a50370cf62f4b1bbe2dc1ee78d99f2d","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fclasate.cimec.ro\u002Fdetaliu.asp?k=3a50370cf62f4b1bbe2dc1ee78d99f2d\" rel=\"noopener\">Brukenthal National Museum\u003C\u002Fa> via Europeana",1058,{"id":653,"source_url":654,"license_code":424,"credit_html":655,"title":7,"description":11,"author":11,"original_width":535,"original_height":536},89091,"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61183","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61183\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",{"id":657,"source_url":658,"license_code":424,"credit_html":659,"title":7,"description":11,"author":11,"original_width":535,"original_height":536},89287,"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61647","Photo: Unknown author — http:\u002F\u002Fcreativecommons.org\u002Flicenses\u002Fby-sa\u002F4.0\u002F, courtesy of \u003Ca href=\"https:\u002F\u002Fgeocollections.info\u002Ffile\u002F61647\" rel=\"noopener\">The Estonian Museum of Natural History\u003C\u002Fa> via Europeana",[],[662,663,664,665,666,667,668,669,670,671,672,673,674,675,676,677,678,679,680,681,682,683,684,685,686,687,688],"Achates unguium colore oculus mundi","Đá opal","Gel-Cristobalite","Gel-pristobalite","Half-Opal","Hemiopal","Hungarian Opal","Indivisible Quartz","Iridot","Lechosopal","Lechosos","Livit","Ljardit","Neslit","Neslita","Neslite","Nevada Opal","Paederos","Pædros","Rumanit","Rumanita","Semiopal","Vidrit","Vidrita","Vidrite","Virgin Valley Opal","White Cliffs Opal",[690,694,698,701,705,709,713,716,721,726,729,733,738,743,747,752,756,759,769,774,777,785,789,793,799,803,806,809,813,816,819,822,826,829,833,839,842,845,850,853,857,862,866,869,873,877,880,884,887,890,893,897,901,904,907,917,921,924,927,930,933,936,939,943,947,951,954,957,960,964,967,971,974,977,981,987,990,993,996,999,1002],{"lang":691,"names":692},"ar",[693],"أوبال",{"lang":695,"names":696},"arz",[697],"اوبال",{"lang":699,"names":700},"az",[7],{"lang":702,"names":703},"bcl",[704],"Opalo",{"lang":706,"names":707},"be",[708],"апал",{"lang":710,"names":711},"bg",[712],"Опал",{"lang":714,"names":715},"bs",[7],{"lang":717,"names":718},"ca",[719,720],"òpal","xilòpal",{"lang":722,"names":723},"cs",[724,725],"drahý opál","opál",{"lang":727,"names":728},"cv",[712],{"lang":730,"names":731},"da",[732],"opal",{"lang":734,"names":735},"de",[736,674,7,737,684],"Amatit","Pyrophan",{"lang":739,"names":740},"el",[741,742],"οπάλιο","οπάλιος",{"lang":744,"names":745},"eo",[746],"opalo",{"lang":748,"names":749},"es",[750,751],"ópalo","opalos",{"lang":753,"names":754},"et",[755],"opaal",{"lang":757,"names":758},"eu",[704],{"lang":760,"names":761},"fa",[762,763,764,765,766,767,768],"اپال","اوپال","چشم گربه","عین الشمس","عین الهر","عین‌الشمس","عین‌الهر",{"lang":770,"names":771},"fi",[772,773],"Opaali","SiO2·nH2O",{"lang":775,"names":776},"fj",[7],{"lang":778,"names":779},"fr",[780,781,782,783,784,686],"Cachalong","opale","Opale AG","Opale commune","Opale potch",{"lang":786,"names":787},"ga",[788],"ópal",{"lang":790,"names":791},"gl",[792],"Ópalo",{"lang":794,"names":795},"he",[796,797,798],"אופאל","אופל","לשם",{"lang":800,"names":801},"hi",[802],"ओपल",{"lang":804,"names":805},"hr",[7],{"lang":807,"names":808},"hu",[725],{"lang":810,"names":811},"hy",[812],"Օպալ",{"lang":814,"names":815},"id",[7],{"lang":817,"names":818},"ilo",[7,792],{"lang":820,"names":821},"io",[704],{"lang":823,"names":824},"is",[825],"Ópall",{"lang":827,"names":828},"it",[781],{"lang":830,"names":831},"iu",[832],"ᐆᐸᓪ",{"lang":834,"names":835},"ja",[836,837,838],"オパール","オパル","蛋白石",{"lang":840,"names":841},"kge",[7],{"lang":843,"names":844},"kk",[712],{"lang":846,"names":847},"ko",[848,849],"단백석","오팔",{"lang":851,"names":852},"ky",[712],{"lang":854,"names":855},"la",[856],"Opalus",{"lang":858,"names":859},"lt",[860,861],"Inversinis opalas","Opalas",{"lang":863,"names":864},"lv",[865],"opāls",{"lang":867,"names":868},"mk",[712],{"lang":870,"names":871},"mn",[872],"Гэрэлт чимэд",{"lang":874,"names":875},"ms",[876,7],"Baiduri",{"lang":878,"names":879},"nb",[732],{"lang":881,"names":882},"nl",[883,755],"Hyaliet",{"lang":885,"names":886},"nn",[732],{"lang":888,"names":889},"no",[7],{"lang":891,"names":892},"pl",[732],{"lang":894,"names":895},"pnb",[896],"اوپل",{"lang":898,"names":899},"pt",[900],"opala",{"lang":902,"names":903},"pt-br",[900],{"lang":905,"names":906},"ro",[732],{"lang":908,"names":909},"ru",[910,911,912,913,914,915,916],"Гиалит","Гидрофан","Джиразоль","Ирисопал","Кахолонг","опал","Солнечный камень",{"lang":918,"names":919},"sah",[920,712],"Опаал",{"lang":922,"names":923},"sh",[7],{"lang":925,"names":926},"sk",[725],{"lang":928,"names":929},"sl",[732],{"lang":931,"names":932},"sr",[915],{"lang":934,"names":935},"sr-ec",[915],{"lang":937,"names":938},"sr-el",[732],{"lang":940,"names":941},"sv",[7,942],"Opalisera",{"lang":944,"names":945},"ta",[946],"அமுதக்கல்",{"lang":948,"names":949},"th",[7,950],"โอปอล",{"lang":952,"names":953},"tl",[7,704],{"lang":955,"names":956},"tr",[7],{"lang":958,"names":959},"uk",[712],{"lang":961,"names":962},"ur",[896,963],"اوپل (جواہر)",{"lang":965,"names":966},"uz",[7],{"lang":968,"names":969},"vi",[663,7,970],"Opan",{"lang":972,"names":973},"war",[704],{"lang":975,"names":976},"wuu",[838],{"lang":978,"names":979},"yue",[980],"澳寶",{"lang":982,"names":983},"zh",[984,838,985,986],"澳宝","貓眼石","閃山雲",{"lang":988,"names":989},"zh-cn",[838],{"lang":991,"names":992},"zh-hans",[838],{"lang":994,"names":995},"zh-hant",[838],{"lang":997,"names":998},"zh-hk",[838],{"lang":1000,"names":1001},"zh-sg",[838],{"lang":1003,"names":1004},"zh-tw",[838],"Q171058",{"history":1007,"applications":1011},{"markdown":1008,"model_version":1009,"prompt_version":1010,"reviewed_at":11},"The name **opal** is one of the oldest gem names still in everyday use. Most modern sources trace it back to the Sanskrit *upala*, meaning *precious stone* or simply *stone*[1]. From Sanskrit it passed into Latin as *opalus*, the form Pliny the Elder used when he wrote about the gem between 75 and 79 CE[2]. A Greek route through *opallios* is sometimes proposed, but the Greek references appear later than the Roman ones[3]. Pliny also used a separate Latin name, *paederos*. Closer modern reading suggests it did not refer to the gem we call opal today[4].\n\nPliny's account in his *Natural History* is the source of the most famous opal story in antiquity. He ranked opal among the most valuable of all gemstones in the Empire[5], and described its play of light in lines gem dealers still quote: *\"for in them you shall see the living fire of ruby, the glorious purple of the amethyst, the sea-green of the emerald, all glittering together in an incredible mixture of light\"*[6]. He also told of the senator Nonius, who owned an almond-sized opal that Mark Antony coveted. When Nonius refused to sell, Antony forced him into exile rather than yield the stone[7]. The Romans ranked opal second only to emerald among precious stones[8].\n\nFor most of the next eighteen centuries, the precious opal that reached European jewellers came from a single district: **Červenica**, in what is now eastern Slovakia, beyond the old Roman frontier[9]. The mines there were worked until the late nineteenth century[9]. The gem held its courtly status throughout — in 1584 Sir Christopher Hatton presented Queen Elizabeth I with an opal *parure*, a full set of matching jewellery[10].\n\nThat reputation almost did not survive the nineteenth century. In 1829 Sir Walter Scott published *Anne of Geierstein*, a novel built around an opal talisman that turned colourless when touched by holy water and killed its wearer[11]. The literary association was enough to crater the market. The sale of opals in Europe fell by about half, and stayed there for roughly twenty years[11].\n\nAustralian discoveries reset the trade. From the 1880s onward, deposits opened at **White Cliffs** in New South Wales, then at **Lightning Ridge** — the source of black opal, with a dark grey to blue-black background[12]. **Coober Pedy** and **Andamooka** followed in South Australia, and the boulder-opal fields of western Queensland around Jundah and Quilpie[12]. By the twentieth century Australia was supplying 95 to 97 percent of the world's precious opal, with South Australia alone accounting for about 80 percent[13]. The largest and most valuable gem opal ever recovered, the *Olympic Australis*, was unearthed at Coober Pedy in 1956 and weighs about 17,000 carats[14].\n\nTwo further sources joined the map later. The volcanic deposits around **Querétaro** in Mexico became, and remain, the most famous source of fire opal[15]. And in 2008 a new find near **Wegeltena** in the Wollo province of Ethiopia produced *Welo* opal — light-bodied and often with vivid play-of-colour[16]. In style it sits closer to Australian sedimentary opals than to the Mexican volcanic kind.","claude-opus-4-7","1.7.0",{"markdown":1012,"model_version":1009,"prompt_version":1010,"reviewed_at":11},"Opal is the gemstone the chemistry textbook is unsure how to classify. Its formula, SiO₂·nH₂O, is hydrated silica — chemically the same family as quartz, but assembled differently. Amorphous opal (opal-A) has no crystal lattice at all[1]. Opal-CT and opal-C are built from nanometre-scale crystals of cristobalite and tridymite — two high-temperature forms of silica[1]. Because the amorphous variety lacks a proper crystal structure, opal is classed as a **mineraloid** rather than a true mineral[2]. That split is what divides the two industries that use it.\n\n### As a gemstone\n\nThe defining feature of **precious opal** is *play-of-colour* — the iridescent flashes of red, green and blue that shift as the stone is turned[3]. The effect is structural, not pigment-based. Silica nanospheres roughly 150 to 300 nanometres across stack into a regular array[3]. That array diffracts visible light the way a thin film does on soap or oil. **Common opal** is built from the same hydrated silica but lacks the ordered spheres, and so has no play-of-colour[4].\n\nSeveral named varieties trade on this difference. **Black opal**, mined mainly at Lightning Ridge in New South Wales, has a dark grey to blue-black background that makes the play-of-colour read especially bright[5]. **Fire opal** is transparent to translucent with warm body colours running from yellow through orange to red, often with no play-of-colour at all[6]. The most famous source of fire opal is Querétaro in Mexico[6]. **Boulder opal**, from western Queensland, occurs as concretions and fracture fillings in a dark siliceous ironstone matrix[7]. Gem and matrix are cut and polished together.\n\nPrecious opal is almost always cut as a *cabochon* — a smooth dome rather than a faceted stone[8]. Play-of-colour is a surface effect, and flat facets would chop it up. Thin or fragile slices are mounted into composite gems. **Doublets** pair an opal slice with a dark backing; **triplets** add a protective quartz cap on top. Doublets and triplets are not classed as precious gemstones in their own right[8]. Australia supplies 95 to 97 percent of the world's precious opal, with South Australia alone responsible for about 80 percent[9].\n\n### As an industrial silica\n\nThe other industry uses opal of a very different kind. **Diatomaceous earth** — also called diatomite — is a soft, light sedimentary rock[10]. It is made almost entirely of the fossil shells of diatoms, single-celled algae that build their skeletons from hydrated silica. Mineralogically those shells are common opal, and diatomite as a whole sits in the opal-CT range[10]. The material has multiple industrial uses, the chief ones being filtration and adsorption[10]. Various forms of common opal are also mined for use as abrasives, insulation media, fillers, and ceramic ingredients[11]. None of these uses care about play-of-colour; what they trade on is the silica's porous, high-surface-area microstructure."]