Opal is classified into four types:
Opal-AG Amorphous-Gel (closely packed amorphous silica spheres form a diffraction grating to create Precious Opal).
Opal-AN Amorphous-Network (found as Hyalite)
Transitions between opal-AG, opal-CT and opal-C are common.
Studies at low temperature show that water molecules way be organized into ice-like structure, which includes the cubic ice modification (Eckert et al., 2015).
Visit gemdat.org for gemological information about Opal.
Classification of Opal
4 : OXIDES (Hydroxides, V[5,6] vanadates, arsenites, antimonites, bismuthites, sulfites, selenites, tellurites, iodates)
D : Metal: Oxygen = 1:2 and similar
A : With small cations: Silica family
75 : TECTOSILICATES Si Tetrahedral Frameworks
2 : Si Tetrahedral Frameworks - SiO2 with H2O and organics
7 : Oxides and Hydroxides
8 : Oxides of Si
Physical Properties of Opal
Optical Data of Opal
Chemical Properties of Opal
Synonyms of Opal
Other Language Names for Opal
Varieties of Opal
A variety of Opal with alumina and lime impurities.
Opal formed of thick mounds deposited from hot silica-rich springs.
A yellow-brownish variety of Opal, resembling Amber.
A greenish-blue opal from Peru.
German name for pink opal variety from Peru (Catamarca?).
A precious opal with bands showing a play of colours.
The most precious kind of opal, this variety of precious opal has a dark background colour.
Translucent blue opal with no play of colours. Cause of colour can be light scattering effects or occasionally microscopic admixture of chrysocolla or other minerals. (See also "Andean Opal")
Opal replacing fossil bone.
A variety of Precious Opal found in Queensland, Australia, as cracks or coatings in and around ironstone/sandstone boulders.
|Cat's Eye Opal|
A rare chatoyant form of opal showing a thin line of fire.
A variety of common or precious opal distinguished by its red-brown color.
|Chrysopal (of Schumann)|
A translucent variety of common opal colored apple green by the presence of nickel.
Transparent mexican Precious Opal with an intense play of colours (red, green, blue and yellow).
A type of opal that doesn't show any fire.
|Contra Luz Opal|
A precious opal where the play of colours is only visible when held up to the light.
A transparent to translucent variety of Precious Opal where the colour play is visible both on the surface and in the interior.
A red variety of Opal.
A yellow to orange variety of opal, owing its colour to microscopic inclusions of orpiment and realgar.
A bluish-white translucent opal with reddish reflections. Name dates back to at least 1837. Compare with Girasol Quartz which is named after this material.
A name for yellow or gold-coloured opal
A variety of Precious Opal in which the play of color is arranged in a vivid harlequin, diamond-shaped, or rectangular-shaped pattern.
An unnecessary name for orange-brown opal.
An old name applied to any opal from Europe. Now even more mistakenly used as a name for white opal.
A colourless variety of Opal. Hyalite is opal-AN, an amorphous silica-glass containing about 3-8% water.
A variety of opal that turns translucent or transparent when immersed in water.
An impure dark-red Opal
A brecciated Jasper cemented by opal.
A transparent opal with a gelatinous appearance and a bluish sheen.
A variety with a milky-white background colour.
Another unnecessary name for a colour variety of Opal.
Precious Opal with long thin lightning-like flashes.
A pale yellow opal
A form of opaline silica, from a vegetable origin. Primarily siliceous remains of grasses and diatoms.
|Mexican Fire Opal|
A transparent red opal from Mexico.
A white Opal.
Opal with dendritic inclusions, usually green silicates.
|Mother of Opal|
A sandstone or ironstone with Opal as a cement.
Unnecessary name for Opal from an igneous origin.
A banded Opal resembling Onyx
Oolitic Opal is a variety of opal made up of interlinked spherical grains, or oolites, of opal.
A term for a thin layer of opal on a host rock.
A type of Opal consisting of aggregated spheres of amorphous silica, with water filling the gaps in between. Precious Opal and Potch Opal consist of this kind of structure - the difference being in the regularity of the sizes of the spheres and packing.
Opal-AN is a term for amorphous opal with a glass-like structure (Graetsch, 1994). The "A" in the name stands for amorphous; the subscript "N" is to imply its structure is network-like similar to silica glass; however, it still contains about 3-8% water, ...
A variety of Opal showing agate-like coloured bands.
A type of opal consisting of disordered α-Cristobalite.
A variety of yellow jasper-coloured Opal.
Pseudomorphs of Opal after Serpentine. A local term.
Sandstone boulders with a thin coating of opal.
Pseudomorph of Opal after Ikaite
WIth very small pinhead-sized colour flashes.
Opal filling long cylindrical cavities.
An opal variety with a pitchy lustre
A green opal.
|Precious Fire Opal|
Fire Opal displaying a play of colour.
A valuable gem-variety of opal.
Opal where colour play appears to wander about at random.
Rose to pink Opal.
A smoky-brown opal coloured by inclusions of radiolaria exoskeletons.
|Red Flash Opal|
Precious Opal with red colour flashes that appear and disappear as the stone is turned.
A yellow-brown common opal with a resinous luster.
Opal replacing fossil shells.
A synthetically grown opal
Alluvial pebbles of Opal.
A yellow-to brown opal with a waxy lustre.
Precious Opal with a white background.
Opal that has replaced fossil wood.
Small rounded pebbles of sandstone impregnated with Precious Opal.
|Chalcedony||30 photos of Opal associated with Chalcedony on mindat.org.|
|Quartz||28 photos of Opal associated with Quartz on mindat.org.|
|Calcite||21 photos of Opal associated with Calcite on mindat.org.|
|Topaz||15 photos of Opal associated with Topaz on mindat.org.|
|Goethite||13 photos of Opal associated with Goethite on mindat.org.|
|Cinnabar||12 photos of Opal associated with Cinnabar on mindat.org.|
|Phillipsite||11 photos of Opal associated with Phillipsite on mindat.org.|
|Magnesite||11 photos of Opal associated with Magnesite on mindat.org.|
|Fluorite||10 photos of Opal associated with Fluorite on mindat.org.|
|Ikaite||10 photos of Opal associated with Ikaite on mindat.org.|
Related Minerals - Nickel-Strunz Grouping
Related Minerals - Hey's Chemical Index of Minerals Grouping
Fluorescence of Opal
Opal in petrology
References for Opal
Internet Links for Opal
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