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| Spectacular Opal From Australia. Copyright © JJ Harrison. From the Willems Miner Collection |
Opal
Although it is still regarded as a valid mineral species for historical reasons, Opal is not a true mineral in the accepted sense of the word as it is either composed of Cristobalite and/or Tridymite or composed of amorphous silica.
From Yowah, Queensland, Australia
