THE NAME OPAL IS thought to have been derived from the Latin word opalus, or from the Sanskrit word upala which means ‘stone’, or ‘valuable stone’. In the Roman era the term opalus was used to describe a ‘stone made from several elements’.
Opals are formed when a mineraloid gel is deposited in fissures of rock, such as limonite, sandstone or basalt, at a low temperature. They have also been known to form or replace fossils, one such famous example being ‘Eric’ the 85 per cent complete opalised skeleton of a Pliosaur that was found in Coober Pedy, South Australia. Eric can now be seen on display in the National Opal Collection on Pitt Street in Sydney.
Opals generally have a water content of between three and ten per cent, but it can be found as high as 20 per cent. The colours of opals range through the entire spectrum,
