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Opal is hardened
silica gel, usually containing 5-10% water. It is therefore noncrystalline,
unlike most other gemstones.
Precious Opal shows flashes of color (iridescence),
caused by the regular arrangement of tiny silica spheres. It occurs in
a number of color varieties from white to orange and pink, brilliant greens
and blues. Opals have been imitated in a costly process, such as Gilson
Opal (below).
Boulder Opal, from Queensland, Australia
comes from an Ironstone Matrix, which can be seen on the backside of these
doublets and triplets. Opals are a soft stone and should be cared
for similar to pearls. |
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