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Precious Opal

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Formula:
SiO2 · nH2O
Colour:
Multi-coloured
Lustre:
Vitreous, Sub-Vitreous, Greasy
Hardness:
5½ - 6½
A variety of Opal

A valuable gem-variety of opal.
Most precious opal is opal-AG. It shows a play of colours ("opalescence") that is due to diffraction of light from the regular packing of submicroscopic silica spheres of roughly equal size (Jones et al, 1964; Sanders, 1964). Although the packing of the spheres may be regular, there is neither short-range nor long-range order in this material, and the X-ray powder diffraction pattern is characterized by a distinct broad hump and a possible weak second hump indicative of material that is "X-ray amorphous" (Jones and Segnit, 1971).
Not all precious opal is opal-AG: The diffracting structure and the resulting opalescence may be preserved to some degree when opal-AG transforms to opal-CT by crystallization (Sanders, 1975).
It usually forms from low temperature deposition from groundwaters in cavities in sedimentary and igneous rocks.


Visit gemdat.org for gemological information about Precious Opal.


Classification of Precious Opal

Physical Properties of Precious Opal

Vitreous, Sub-Vitreous, Greasy
Diaphaneity (Transparency):
Translucent
Colour:
Multi-coloured
Streak:
white
Hardness (Mohs):
5½ - 6½
Fracture:
Conchoidal

Chemical Properties of Precious Opal

Formula:
SiO2 · nH2O
Elements listed in formula:

Other Names for Precious Opal

Name in Other Languages:

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

References for Precious Opal

Reference List:
Sanders, S.V. (1964) Colour of precious opal. Nature, 204: 1151-1153.

Jones, J.B., Sanders, J.V., Segnit, E.R. (1964) Structure of opal. Nature, 204: 990-991.

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.

Sanders, J.V. (1975) Microstructure and crystallinity of gem opals. American Mineralogist, 60, 749-757.

Anal. Chem. Acta (1994): 286: 107.

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. American Mineralogist, 93, 1865-1873.

Lapis Extra No. 10, Opal (1996).

Internet Links for Precious Opal

mindat.org URL:
https://www.mindat.org/min-6666.html
Please feel free to link to this page.

Localities for Precious Opal

This map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
(TL) indicates type locality for a valid mineral species. (FRL) indicates first recorded locality for everything else. ? indicates mineral may be doubtful at this locality. All other localities listed without reference should be considered as uncertain and unproven until references can be found.
Australia
 
  • New South Wales
    • Finch Co.
- Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. - Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram. - Australian Opal Centre web site http://www.australianopalcentre.com/
- Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
- Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
- Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. - Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
[var: Black Opal] Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
- Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram. - Australian Opal Centre web site http://www.australianopalcentre.com/
- Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. - Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram. - Australian Opal Centre web site http://www.australianopalcentre.com/
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram.
Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville.
    • Georgiana Co.
W. Curran (1896) Occurrence of precious stones in N.S.W. Journal and Proceedings of the Royal Society of New South Wales, 30, 214-271
    • Narran Co.
      • Angledool
- Smith, E. & R. (1999): Black Opal Fossils of Lightning Ridge - Treasures from the Rainbow Billabong, Kangaroo Press, East Roseville. - Cram, L. (2004): A Journey with Colour, Vol 2, Part B - A History of Lightning Ridge Opal 1873-2003, Len Cram. - Australian Opal Centre web site http://www.australianopalcentre.com/
    • Rous Co.
      • Tintenbar
Smallwood, A. G., Thomas, P., & Ray, A. S. (2008). Comparative analysis of sedimentary and volcanic precious opals from Australia. Journal of Australasian Ceramic Society.
    • Yungnulgra Co.
No reference listed
[var: Boulder Opal]
    • Paroo Shire
    • Quilpie Shire
Rocks & Min.: 8:15.
Rocks & Min.:8:4.
[var: Boulder Opal]
Martins da Pedra collection
    • Winton Shire
[var: Boulder Opal] Dennis Tryon collection
  • South Australia
    • Central North
Georgina Gordon, Brian Morris & Josine Talbot (2014) Logging the Regolith Profile of Cooper Pedy, South Australia. in Geological Society of Australia, 2014 Australian Earth Sciences Convention (AESC), Sustainable Australia. Abstract No 110 of the 22nd Australian Geological Convention
Barnes, L.C., (1992), Opal: South Australia's gemstone, Dept. of Mines and Energy, Geological Survey of South Australia, [Parkside, S. Aust.].
Barnes, L.C., (1992), Opal: South Australia's gemstone, Dept. of Mines and Energy, Geological Survey of South Australia, [Parkside, S. Aust.].
    • North West Province
      • Mintabie district
John Nijhuis.
    • Stuart Shelf
      • Andamooka Ranges
[var: Black Opal] Opal, Lithographie, 2007
  • Western Australia
    • Coolgardie Shire
      • Coolgardie
Fetherston, J. M., Stocklmayer, S. M. and Stocklmayer, V. C. (2013): Gemstones of Western Australia. Mineral Resources Bulletin 25, Geological Survey of Western Australia, Perth, Australia, 306 pp.
    • Kalgoorlie-Boulder Shire
      • Cowarna Downs Station
Fetherston, J., Stocklmayer, S., Stocklmayer, V.(2013): Gemstones of Western Australia, Geological Survey of Western Australia
Brazil
 
  • Pará
    • São Geraldo do Araguaia
Revista Brasileira de Geociências 30(2):251-255, junho de 2000
Canada
 
  • British Columbia
    • Omenica Mining Division
      • Burns Lake
www.em.gov.bc.ca/cf/minfile
      • Troitsa Peak
MINFILE No 093E 120; Simandl, G. J., Paradis, S., Diakow, L. J., Wojdak, P. J., & Hartley, A. J. (1998). PRECIOUS OPAL IN THE WHITESAIL RANGE, WEST-CENTRAL BRITISH COLUMBIA, CANADA (NTS 93E/10W AND 93E/11E). Geological Fieldwork: A Summary of Field Activities and Current Research..., 285.
    • Vernon Mining Division
      • Vernon
www.em.gov.bc.ca/cf/minfile; Simandl, G.J. (2009): Nonmetallic minerals other than coal: Industrial minerals, gemstones and aggregate in British Columbia, Canada; British Columbia Geological Survey, Paper 2009‐2, pages.; Simandl, G. J., Hancock, K. D., Callaghan, B., Paradis, S., & Yorke-Hardy, R. (1997). Klinker Precious Opal Deposit, South Central British Columbia, Canada-Field Observations and Potential Deposit-Scale Controls. British Columbia Ministry of Energy and Mines, 321-327.
Germany
 
  • Saxony
    • Döbeln
H. Vollstädt, R. Baumgärtel: "Einheimische Edelsteine", 2nd. ed., Steinkopff (Dresden), 1977
Honduras
  • Gracias a Dios Department
Rocks & Min.:8:8.
  • Lempira Department
[var: Black Opal] N. Jb. Mineral. Abh. 186 (2009) 11-20.
Hungary
www.giant.net.au/users/bmi/prof.htm.
  • Borsod-Abaúj-Zemplén Co.
    • Zemplén Mts (Tokaj Mts)
      • Erdőhorváti
[var: Black Opal]
[var: Black Opal] Szakáll & Gatter: Hungarian Mineral Species, 1993
      • Komlóska
[var: Black Opal] Koch: Minerals of Hungary, 1985
      • Legyesbénye
[var: Black Opal] Szakáll: Top.Min. Hun.
      • Megyaszó
Szakáll & Jánosi: Minerals of Hungary, 1995
Szakáll: Topographia Mineralogica Hungariae III.
      • Tállya
[var: Black Opal]
      • Telkibánya
Szakáll-Weiszburg: Telkibánya
Indonesia
 
Sujatmiko, Dr H. C. Einfalt, Dr U. Henn (2007) Opal from Java, Indonesia and Its Varieties. http://www.hagi.or.id/paper/opal-from-java-indonesia-and-its-varieties/
    • Banten Province (Bantam Province)
Extra Lapis - English No. 10 Opal
Mexico
 
  • Guanajuato
    • Mun. de Cuerámaro
      • Cuerámaro
Panczner(1987):286.
    • Mun. de Pénjamo
      • Pénjamo
Panczner(1987):287.
  • Jalisco
    • Mun. de Magdalena
      • La Amazata
Panczner(1987):287.
Panczner(1987):287.
      • Magdalena
Panczner (1987): 287.
Panczner (1987): 287.
      • San Andrés
Panczner(1987): 288.
      • San Simón
Panczner(1987):288.
Panczner (1987): 288.
    • Mun. de San Cristóbal de la Barranca
      • El Salvador
Panczner(1987):288.
Panczner(1987):288.
  • Nayarit
    • Mun. de Jalisco
      • La Curva
Panczner(1987):288.
  • Queretaro
    • Mun. de Amealco
      • Amealco
Panczner (1987): 288.
    • Mun. de Ezequiel Montés
      • Ezequiel Montés
Panczner(1987):289.
[var: Contra Luz Opal]
    • Mun. de Tequisquiapan
      • La Trinidad
Panczner(1987):289.
Russia
 
  • Far-Eastern Region
    • Primorskiy Kray
Vysotskiy, S. V., Galkin, N. G., Barkar, A. V., Chusovitin, E. A., & Karabtsov, A. A. (2010). Hydrothermal precious opals of the Raduzhnoe deposit, north Primorye: The nature of the opalescence. Russian Journal of Pacific Geology, 4(4), 347-354.
Slovakia
 
  • Banská Bystrica Region
    • Krupina Co.
      • Hontianske Nemce
Koděra, M. et al., 1986 a 1990 : Topografická mineralógia Slovenska, diel 1- 3, Veda – Vydavateľstvo SAV, Bratislava, 1990, 1 – 1590k
  • Prešov Region
    • Prešov Co.
      • Červenica
        • Dubník
Koděra, M. et al., 1986 a 1990 : Topografická mineralógia Slovenska, diel 1- 3, Veda – Vydavateľstvo SAV, Bratislava, 1990, 1 – 1590
Koděra, M. et al (1986): Topografická mineralógia Slovenska. VEDA - vydavateľstvo SAV, 1986, part 1, page 257 - 274
Koděra, M. et al., 1986 a 1990 : Topografická mineralógia Slovenska, diel 1- 3, Veda – Vydavateľstvo SAV, Bratislava, 1990, 1 – 1590
Somaliland
 
Wolfgang Hampel specimen
  • Jodha
Journal of Gemmology, 28:81-84 (2002).
Spain
 
  • Canary Islands
    • Las Palmas Province
Extra Lapis - English No. 10 Opal
  • Catalonia
    • Girona (Gerona)
      • La Selva
        • Caldes de Malavella
Joaquim Mollfulleda, Minerales, Omega, 1996
        • Sils
          • Massabè
Joaquim Mollfulleda, Minerales, Omega, 1996
USA
 
  • Arizona
    • Maricopa Co.
      • Vulture Mts
        • Vulture District
Galbraith, F.W. & D.J. Brennan (1959), Minerals of AZ: 87.
    • Santa Cruz Co.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd.ed.: 193.
      • Oro Blanco Mts
        • Oro Blanco District (Ruby District)
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd.ed.: 193.
      • Redrock District
        • Redrock Canyon
          • East of Red Rock Canyon
Lewis, W. Scott (1942), Gem collecting in California: Hobbies: 47: 116-117; Murdoch, Joseph & Robert W. Webb (1966), Minerals of California, Centennial Volume (1866-1966): California Division Mines & Geology Bulletin 189: 282.
    • Yavapai Co.
      • Bradshaw Mts (Bradshaw Range)
        • Castle Creek District
Galbraith, F.W. & D.J. Brennan (1959), Minerals of AZ: 87.
  • Arkansas
    • Garland Co.
      • Wilson Springs (Potash Sulfur Springs)
        • Union Carbide Mine
R&M 70:3 pp 154-170
  • California
    • Kern Co.
      • El Paso Mts
        • El Paso Mountains District
          • Last Chance Canyon
            • Silica Gem claims
Christopher N. Wentzell
Christopher Wentzell
    • Napa Co.
      • Knoxville District
        • Knoxville
  • Idaho
    • Clark Co.
      • Spencer
Extra Lapis - English No. 10 Opal
Extra Lapis - English No. 10 Opal
    • Latah Co.
The Moscow Opal Mines 1890 to 1893 (The First Commercial Opal Mines in the United States), Ron Brockett, 1975
Dake, 1956. NW Gem Trails, 2nd ed.
    • Lemhi Co.
      • Salmon
Extra Lapis - English No. 10 Opal
    • Owyhee Co.
Dake, 1956. NW Gem Trails, 2nd ed.
  • Louisiana
    • Vernon Parish
R&M 69:3 pp 156-162
  • Nebraska
    • Custer Co.
The Minerals and Gemstones of Nebraska CSD U Neb EC 2
    • Furnas Co.
The Minerals and Gemstones of Nebraska CSD U Neb EC 2
    • Morrill Co.
The Minerals and Gemstones of Nebraska CSD U Neb EC 2
  • Nevada
    • Humboldt Co.
      • Donnelly District
NBMG Spec. Pub. 31 Minerals of Nevada
NBMG Spec. Pub. 31 Minerals of Nevada
NBMG Spec. Pub. 31 Minerals of Nevada
      • Santa Rosa Range
NBMG Spec. Pub. 31 Minerals of Nevada
      • Virgin Valley
[var: Black Opal] [www.johnbetts-fineminerals.com]
NBMG Spec. Pub. 31 Minerals of Nevada; USGS Bull 1538D
Christopher Wentzell
Eckert, Allen W. (1997) The World of Opals. (John Wiley & Sons, New York). p. 312,310.
Rocks & Min.:13:56.; USGS Bull 1538D
Christopher Wentzell collection.
USGS Bull 1538D
Christopher Wentzell
NBMG Spec. Pub. 31 Minerals of Nevada
USGS Bull 1538D
Rocks & Min.: 8:16; 19:13.; USGS Bull 1538D
Keith Hodson, (1994) personal communication to Christopher Wentzell
USGS Bull 1538D
NBMG Spec. Pub. 31 Minerals of Nevada
Christopher Wentzell;
          • WRT Stonetree group ("Dominion Opal Mine")
Christopher Wentzell collection.
Sinkankas, John (1959) Gemstones of North America. Figure 30 at page 116.
Christopher N. Wentzell
various contributors (2013) Nevada-Jackpot! Mineral Monograph 18, Lithographie LLC, 59
    • Lincoln Co.
      • Mormon Mts
        • Mormon Mountains District
NBMG Spec. Pub. 31 Minerals of Nevada
    • Nye Co.
NBMG Spec. Pub. 31 Minerals of Nevada
  • New Mexico
    • Grant Co.
      • Central District
Minerals of New Mexico 3rd ed.
Minerals of New Mexico 3rd ed.
    • Sandoval Co.
NMBMMR Bull 81 Summary of the Mineral Resources of Bernalillo, Sandoval, and Santa Fe Counties, New Mexico
  • Oregon
    • Lake Co.
Dake, 1956. NW Gem Trails, 2nd ed.
    • Morrow Co.
Extra Lapis - English No. 10 Opal
  • Texas
    • Brewster Co.
      • Alpine
http://www.omsinc.org/archives/Ore-cutts_Jan04.pdf
  • Washington
    • Whitman Co.
      • Pullman
Dake, 1956. NW Gem Trails, 2nd ed.
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