Gemmology
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Opal — specimens [gallery view]


Regarded as mineral species for historical reasons; not a true mineral in the accepted sense of the word as it is either composed of cristobalite and/or tridymite or of amorphous silica; sedimentary and secondary from the alteration of high silica igneous extrusive rocks. There are specimens of 2610 carats (Arem, 1987: 139).
Opal — specimen 0376
0376
Mexico
Opal — specimen 0417
0417
Mexico
Opal — specimen 0167
0167
Mexico
Opal — specimen 0412
0412
Mexico
Opal — specimen 0211
0211
Mexico
Opal — specimen 0227
0227
Mexico
Opal — specimen 0544
0544
Madagascar
Opal — specimen 0722
0722
Mexico
Opal — specimen 0229
0229
Madagascar
Opal — specimen 0264
0264
Madagascar

Opal — specimens — 40
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