Opal-A
A variety of Opal
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About Opal-A
A variety of Opal
X-Ray amorphous opal (hydrous silica), sometimes divided into two subtypes:
——— Opal-AG: (Amorphous-Gel) (contains closely packed amorphous silica spheres, which at times form a diffraction grating to create precious opal). Since the packing of the spheres is similar to the structure of a gel, the subscript G ("gel-like") has been added (Flörke et al, 1991; Graetsch, 1994).
——— Opal-AN: (Amorphous-Network (commonly found as hyalite). It still contains spheres, but much smaller (Lee et al., 2022) and lacks a play of colours.
In the study of Lee et al. (2022) opal-AN was shown to mainly comprise aggregates of differently-sized nanospheres (<5 nm) that form banded features. The opal-AG studied comprised close-packed silica nanospheres, ~400 nm in diameter, and these can be ordered into regular layers which can diffract light, causing the play of colour in most precious opal (Jones et al, 1964; Sanders, 1964 & 1968).
X-Ray amorphous opal (hydrous silica), sometimes divided into two subtypes:
——— Opal-AG: (Amorphous-Gel) (contains closely packed amorphous silica spheres, which at times form a diffraction grating to create precious opal). Since the packing of the spheres is similar to the structure of a gel, the subscript G ("gel-like") has been added (Flörke et al, 1991; Graetsch, 1994).
——— Opal-AN: (Amorphous-Network (commonly found as hyalite). It still contains spheres, but much smaller (Lee et al., 2022) and lacks a play of colours.
In the study of Lee et al. (2022) opal-AN was shown to mainly comprise aggregates of differently-sized nanospheres (<5 nm) that form banded features. The opal-AG studied comprised close-packed silica nanospheres, ~400 nm in diameter, and these can be ordered into regular layers which can diffract light, causing the play of colour in most precious opal (Jones et al, 1964; Sanders, 1964 & 1968).
Unique Identifiers
Mindat ID:
47868 (as Opal-A)
3004 (as Opal)
3004 (as Opal)
Long-form identifier:
mindat:1:1:47868:7 (as Opal-A)
mindat:1:1:3004:1 (as Opal)
mindat:1:1:3004:1 (as Opal)
GUID
(UUID V4):
(UUID V4):
f661978f-61bd-480a-86ca-b534967be2a3 (as Opal-A)
b3226449-9ed0-47fe-a88a-e53851c6d480 (as Opal)
b3226449-9ed0-47fe-a88a-e53851c6d480 (as Opal)
Varieties of Opal-A
Opal-AG | 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 | 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, ... |
Common Associates
Associated Minerals Based on Photo Data:
3 photos of Opal-A associated with Quartz | SiO2 |
2 photos of Opal-A associated with Sinter | |
1 photo of Opal-A associated with Chabazite | |
1 photo of Opal-A associated with Calcite | CaCO3 |
1 photo of Opal-A associated with Jarosite | KFe3+3(SO4)2(OH)6 |
1 photo of Opal-A associated with Akaganeite | (Fe3+,Ni2+)8(OH,O)16Cl1.25 · nH2O |
1 photo of Opal-A associated with Kalinite | KAl(SO4)2 · 11H2O |
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.
Opal-A in petrology
An essential component of rock names highlighted in red, an accessory component in rock names highlighted in green.
Internet Links for Opal-A
mindat.org URL:
https://www.mindat.org/min-47868.html
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References for Opal-A
Reference List:
Localities for Opal-A
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).
Struck out - Mineral was erroneously reported from this locality.
Faded * - Never found at this locality but inferred to have existed at some point in the past (e.g. from pseudomorphs).
All localities listed without proper references should be considered as questionable.
All localities listed without proper references should be considered as questionable.
Valeč Hyalite occurrences, Valeč, Karlovy Vary District, Karlovy Vary Region, Czech Republic