Formation
Opal is formed from silicon dioxide and water,it is not like other gemstones as they are made from crystals,for example diamonds.
Opal occurs at Lightning Ridge as irregular nodules (nobbies) or in seams and thin layers within vertical or horizontal joint planes, in a characteristic soft, grey to buff-coloured claystone. Opal is often found near the junction of the claystone and overlying sandstone.
As water flows down into the earth it picks up silica and sandstone and flows into cracks and crevices left by naturally forming faults where it is deposited. As the water evaporates silica is left behind. If the water evaporates to quickly it forms "colourless potch",if the evaporation process is slower and under much pressure,quality opal known as precious opal is created.
Opal occurs at Lightning Ridge as irregular nodules (nobbies) or in seams and thin layers within vertical or horizontal joint planes, in a characteristic soft, grey to buff-coloured claystone. Opal is often found near the junction of the claystone and overlying sandstone.
As water flows down into the earth it picks up silica and sandstone and flows into cracks and crevices left by naturally forming faults where it is deposited. As the water evaporates silica is left behind. If the water evaporates to quickly it forms "colourless potch",if the evaporation process is slower and under much pressure,quality opal known as precious opal is created.
