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. This cycle repeats over very long periods of time, and eventually opal is formed.
It’s believed that perhaps 30 million years ago, lots of silica was released into a solution which filled cracks in the rocks, layers in clay, and even some fossils. Some of them became precious opals. It takes about 5 to 6 million years to make a 1 cm opal to mature.
Where do most Opals come from?
More than 90% of the world’s precious opals come from Australia, and the rest can be found in other parts of the world such as Mexico, Brazil, Indonesia, Czech Republic, Ethiopia and USA.
How much are Opals Worth?
Generally opals with a black or dark body tone are more valuable than those with a white, light, or crystal body tone, because a stone with a darker body tone tends to display colours more vibrantly. Each stones is as unique as the next so prices can vary. The price is usually determined by the colours that shine through the stone. Black opal is the most prized opal and may realise prices over AUD $15,000 a carat.
Opal is the birthstone of October.
Opal has been found on Mars!
Queen Victoria’s favorite gemstone was Opal!