Precious Opal
A variety of Opal
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About Precious Opal
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.
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.Unique Identifiers
Mindat ID:
6666 (as Precious Opal)
3004 (as Opal)
3004 (as Opal)
Long-form identifier:
mindat:1:1:6666:8 (as Precious Opal)
mindat:1:1:3004:1 (as Opal)
mindat:1:1:3004:1 (as Opal)
GUID
(UUID V4):
(UUID V4):
73b847cc-22db-4ea7-ba1d-1e0844734972 (as Precious Opal)
b3226449-9ed0-47fe-a88a-e53851c6d480 (as Opal)
b3226449-9ed0-47fe-a88a-e53851c6d480 (as Opal)
Pronunciation of Precious Opal
Pronunciation:
| Play | Recorded by | Country |
|---|---|---|
| Jolyon Ralph | United Kingdom |
Physical Properties of Precious Opal
Vitreous, Sub-Vitreous, Greasy
Transparency:
Translucent
Colour:
Multi-coloured
Streak:
white
Hardness:
5½ - 6½ on Mohs scale
Fracture:
Conchoidal
Chemistry of Precious Opal
Mindat Formula:
SiO2 · nH2O
Elements listed:
Synonyms of Precious Opal
Varieties of Precious Opal
| Bandfire Opal | A precious opal with bands showing a play of colours. |
| Black Opal | The most precious kind of opal, this variety of precious opal has a dark background colour. |
| Boulder Opal | A variety of Precious Opal found in Queensland, Australia, as cracks or coatings in and around ironstone/sandstone boulders. |
| Claro Opal | Transparent mexican Precious Opal with an intense play of colours (red, green, blue and yellow). |
| Contra Luz Opal | A precious opal where the play of colours is only visible when held up to the light. |
| Crystal Opal | A transparent to translucent variety of Precious Opal where the colour play is visible both on the surface and in the interior. |
| Harlequin Opal | A variety of Precious Opal in which the play of color is arranged in a vivid harlequin, diamond-shaped, or rectangular-shaped pattern. |
| Lechosos Opal | A variety with a milky-white background colour. |
| Levin Opal | Precious Opal with long thin lightning-like flashes. |
| Mother of Opal | A sandstone or ironstone with Opal as a cement. |
| Opal Matrix | A term for a thin layer of opal on a host rock. |
| Painter Boulder | Sandstone boulders with a thin coating of opal. |
| Pinfire Opal | WIth very small pinhead-sized colour flashes. |
| Pyrophane | Opal where colour play appears to wander about at random. |
| Red Flash Opal | Precious Opal with red colour flashes that appear and disappear as the stone is turned. |
| White Opal | Precious Opal with a white background. |
| Yowah Nut | Small rounded pebbles of sandstone impregnated with Precious Opal. Originally reported from Yowah opal field, Queensland, Australia. |
Common Associates
Associated Minerals Based on Photo Data:
| 79 photos of Precious Opal associated with Petrified Wood | |
| 26 photos of Precious Opal associated with Opal | SiO2 · nH2O |
| 18 photos of Precious Opal associated with Black Opal | SiO2 · nH2O |
| 9 photos of Precious Opal associated with Boulder Opal | SiO2 · nH2O |
| 6 photos of Precious Opal associated with Milk Opal | SiO2 · nH2O |
| 4 photos of Precious Opal associated with Harlequin Opal | |
| 3 photos of Precious Opal associated with Opal Matrix | |
| 3 photos of Precious Opal associated with Shell Opal | |
| 2 photos of Precious Opal associated with Fire Opal | SiO2 · nH2O |
| 2 photos of Precious Opal associated with Bone Opal | SiO2 · nH2O |
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.
Internet Links for Precious Opal
mindat.org URL:
https://www.mindat.org/min-6666.html
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References for Precious Opal
Reference List:
Jones, J. B., Segnit, E. R. (1971) The nature of opal I. nomenclature and constituent phases. Journal of the Geological Society of Australia, 18 (1) 57-68 doi:10.1080/00167617108728743
Localities for Precious Opal
symbol to view information about a locality.
The Locality List
- This locality has map coordinates listed.
- This locality has estimated coordinates.
ⓘ - Click for references and further information on this occurrence.
? - Indicates mineral may be doubtful at this locality.
- Good crystals or important locality for species.
- World class for species or very significant.
(TL) - Type Locality for a valid mineral species.
(FRL) - First Recorded Locality for everything else (eg varieties).
All localities listed without proper references should be considered as questionable.
Quilpie, Quilpie Shire, Queensland, Australia