Opal is a hydrated amorphous form of silica (SiO2·nH2O); its water content may range from 3 to 21% by weight but is usually between 6 and 10%. Because of its amorphous character, it is classed as a mineraloid, unlike crystalline forms of silica, which are classed as minerals.
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| inclusions in wood opal |
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| Iron sulfide in opal |
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| fern like a holographic play of colour patterns in opal |
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| pyrite inclusions in opal |
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| Iron oxide in opal |
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| opal from USA |
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| Clay mineral along with pyrite in opal |
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| Play of colour in opal |
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| Manganese oxide flower in opal |
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| Iron oxide in opal |
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| Chalcedony along with amphibole needles in opal |
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| Green opal |
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| Manganese oxide in opal |
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| Manganese oxide in opal |
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| fluorite inclusions in opal |
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| opal from Ethiopia |
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| wood in opal |
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| Agate like banding pattern in opal |
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| Leopard opal |
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| Conk opal |
The same slides are in the form of video uploaded on youtube.
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