A variety of
OpalThis material should be properly labelled as
Opal-AN
An often-colourless variety of
Opal found as globular concretions. It is an amorphous silica-glass containing water. It is often refered to by the common name 'Hyalite'.
This form of opal occurs in volcanic and pegmatite environments where the silica deposits at elevated temperatures. The "A" in the name stands for amorphous; the subscript "N" is to imply its structure is network-like similar to silica glass rather than composed of separate gel spheres; however, it still contains significant water.
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