Opal is a gemstone whose chemical composition is an amorphous, gelatinous, hydrous silica containing varying degrees of water and traces of metal oxides. The opal called fire opal is often carved, engraved or faceted.

There are two varieties of opal : the iridescent precious opal, known also as the noble opal, and the milky white common opal.

-see also:
"Opal" is in the UNSPSC Code "54121603"
  Opal gemstones

Ref: 123977/2006-10-18

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List of books: Opal

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