What Makes Opal So Unique ?
Australia’s National Gemstone
Precious opal is Australia’s national gemstone. Since the early days of opal mining in central Australia in the 1870’s, opal has become part of the economic fabric and cultural identity of Australia’s Great Artesian Basin (GAB).
Other Sources Of Opal
Virgin Valley, Nevada
What Is Opal Made Of ?
Opal is formed from silicon dioxide and water (SiO2·nH2O) . Scientists agree that opal is formed by the settling of the tiny silica based spheres out of a gel or liquid into cracks and fissures in rocks.
Where Is Opal Found ?
Open Cavities In Ironstone (Boulder Opal, e.g. Queensland Boulder)
Replacing Clay In Sandstone Pore Spaces (Matrix Opal, e.g. Boulder Matrix and Andamooka Matrix)
Replacing Clay Pebbles (e.g. Yowah Nuts found in Queensland)
Replacing Minerals Fossils (e.g. opalised fossils)
Opal On Mars !?
Opal has been recently found on Mars. Scientists used high-powered scanning electron microscopy to examine a fragment of a Martian meteorite known as Nakhla. This meteorite fell to Earth in Egypt in 1911.
Similar to the GAB, the surface of Mars is largely covered by sediments eroded from volcanic rocks. Mars’ surface also lacks significant amounts of carbonate and went through a major and final period of dehydration. The reddish color of Mars suggests that oxidative acidic weathering played an important role during and after dehydration of the surface..The discovery of opal in the meteorite confirms that the same acidic weathering that formed opal in the GAB also occurred on Mars.
The type of opal found in the meteorite is known as “Fire Opal“ because of its vivid orange, yellow and red colors.