A Geoscience Digital Image Library
A Geoscience Digital Image Library
| Title | Opal |
|---|---|
| Description | Opal is considered a mineraloid because its structure is not truly crystalline. It has chemistry SiO2-nH2O. The amount of water, 5-10% or greater, is controlled by the temperature of the host rock at the time the opal formed. Opal forms in sedimentary environments and as a secondary mineral in high-silica extrusive rocks. The most striking quality of opal is its ability to refract and reflect specific wavelengths of light, giving it the characteristic “opalescence”. In this sample, the opalescence is only weekly developed. Opal's name comes from the Old Indian upala meaning “precious stone”. |
| Location | USA ▹ Texas |
| Photographer | Shannon Heinle. 2001-06-12. |
| Collection | University of North Dakota Mineralogy Collection #1622. |
| Key words | opal, mineraloid |
| Tech details | 440 KB. Hand specimen. Fujifilm FinePix S1Pro digital camera; 60mm AF Nikon micro lens. |
| GeoDIL number | 710 |
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