Opal

Crystals buys its range of opals from the extremely hot, dry centre of Australia where the opal miners not only extract opal underground, their houses are also underground!

Opals form very slowly in sedimentary rocks (e.g. sandstone) where water is present.

Hydrated silica: SiO2·n(H2O)

No crystal structure, instead a regular arrangement of miniscule silica spheres which diffract, or scatter, light. Variations in sphere size determine the range of colours seen.

More precious opals all show some internal ‘colour play’ or ‘flashes’. Blue/green opals are very popular but those containing reds, oranges or violets usually demand a premium. ‘Fire opals’ refer to red/orange clear opals (NOT from the internal flashes mentioned above).

The particular characteristics of opals mean that certain rules must be followed to keep the stones in good condition:

Avoid scratching the relatively soft surface.

Avoid very high temperatures (e.g. very hot water) or extreme low humidity (e.g., bank vaults!).

Clean, if necessary, with mild detergent and a damp cloth or soft toothbrush.

If storing for long periods, pop in cotton wool in a sealed plastic bag with a few drops of water.

Pliny, in Roman times, described opal as having ‘the fire of the ruby, the brilliant purple of the amethyst, and the sea-green of the emerald, all shining together in incredible union’.

The Arabs believed opals fell from heaven in flashes of lightning, gaining their fiery flashes as they fell.