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SiO2 · nH2O
colourless, white, creme-coloured
5½ - 6½
Specific Gravity:
2.0 - 2.2
A variety of Opal

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, both as molecular water and bound in silanole (SiOH) groups.

This form of opal occurs as hyalite in volcanic and pegmatite environments where the silica deposits from the gas phase (Flörke et al, 1973) and forms globular and irregular crusts. Because of its homogeneous internal structure, it does not show opalescence and is transparent if pure. The refractive index varies slightly with water content and lies between 1.44 and 1.46 (Graetsch, 1994).

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Physical Properties of Opal-ANHide

Transparent, Translucent
colourless, white, creme-coloured
no opalescence (play of colour)
5½ - 6½ on Mohs scale
None Observed
2.0 - 2.2 g/cm3 (Measured)    
varies with water content

Chemical Properties of Opal-ANHide

SiO2 · nH2O

Synonyms of Opal-ANHide

Other Language Names for Opal-ANHide

Common AssociatesHide

Associated Minerals Based on Photo Data:
Quartz132 photos of Opal-AN associated with Quartz on
Fluorite131 photos of Opal-AN associated with Fluorite on
Schorl130 photos of Opal-AN associated with Schorl on
Muscovite79 photos of Opal-AN associated with Muscovite on
Feldspar Group78 photos of Opal-AN associated with Feldspar Group on
Smoky Quartz78 photos of Opal-AN associated with Smoky Quartz on
Carbonate-rich Fluorapatite63 photos of Opal-AN associated with Carbonate-rich Fluorapatite on
Aquamarine47 photos of Opal-AN associated with Aquamarine on
Orthoclase46 photos of Opal-AN associated with Orthoclase on
Topaz44 photos of Opal-AN associated with Topaz on

Other InformationHide

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 Opal-ANHide

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Flörke, O.W., Jones, J.B., Segnit, E.R. (1973) The genesis of hyalite. Neues Jahrbuch der Mineralogie, Monatshefte, H.2, 82-89.
Graetsch, H. (1994) Structural characteristics of opaline and microcrystalline silica minerals. In: Reviews in Mineralogy, Volume 29, Silica - Physical behavior, geochemistry and materials applications. Mineralogical Society of America, Washington, D.C.

Internet Links for Opal-ANHide

Localities for Opal-ANHide

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.

Locality ListShow

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