Aussie ABC: O is for Opal!

I didn’t understand all the fuss about SiO2.nH2O until 2004. That’s when I first visited Coober Pedy – slap bang in the middle of absolutely freakin nowhere in the South Australian Outback – and found a piece of SiO2.nH2O I wanted to take home with me. But you might know SiO2.nH2O better as Hydrous Silica. Or maybe Opal! Down here,
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