For those of you born in the autumnal month of October, opal is your birthstone.
Opal is a hardened silica gel, containing up to 10 per cent water and formed in cavities within rocks. There are two varieties: precious opal – the most desirable, which shows flashes of colour (iridescence) – and the common or ‘potch’ opal.
Until the 19th Century, Slovakia was the primary source of origin until large deposits were found in Australia, including the rare and prized black opal.
Australian opal has often been cited as accounting for 95–97% of the world’s supply of precious opal. Recent data suggests that the world supply of precious opal may have changed. In 2012, Ethiopian opal production was estimated to be 14,000 kg, for example.
Through historic folklore, opal was believed to bring the wearer the power of invisibility, to bring happy dreams and to ease the process of change.