When was opal first found and where?
First found in Hungary (Europe) during Roman Empire.
Opals – What is it and where does it come from ?
Opal is formed from a solution of silicon dioxide and water. As water runs down through the earth, it picks up silica from sandstone, and carries this silica-rich solution into cracks and voids , caused by natural faults or decomposing fossils.
As the water evaporates, it leaves behind a silica deposit.
Opal is made from silica combined with water.
Opal is a non-crystalline form of the mineral silica and is formed from amorphous “balls” or “lumps” of silica.
The opal fields of Australia are in the harsh outback where only the hardened miner can make a living.
Opal Locations in Australia
Black Opal comes from Lightning Ridge in New South Wales – approx 9 hrs drive. Light or White Opal is mined principally from the South Australian fields of Mintabie, Coober Pedy and Andamooka.
How is it formed?
Opal formation begins as water filters through silica-rich rock, dissolving some of the silica. When that water passes through a cavity in a suitable rock, the silica precipitates as a film on the wall of the cavity. After tens of millions of years, say the scientists, you will have an opal.
Now opals have been found along with fossilised soil bacteria, similar to typical soil bacteria you find today. With this finding, some scientists have suggested that the acids produced by the bacteria may have helped form the opals. They propose that the acids produced by the bacteria dissolved some of the minerals in nearby feldspar, forming the opals. Obviously, this process would not take as long as the purely natural process traditionally thought to form opals.
Other geologists are reluctant to give bacteria any credit for opal formation. However, one opal expert, Dr. Len Cram, has been growing opals in a process that takes only a few months. It is called Cultured Opal.
WHAT IS POTCH??
ANSWER : OPAL WITH NO COLOUR
Potch is what precious opal is formed on. It can be grey, black or even white in colour.
The majority of common opal mined is called Potch, so it is basically common opal with no colour.