Twin Opal Pineapple
Rare Double Opal Pineapple
Double Opal Pineapple [ SiO2nH2O ]
In Australia, precious opal is found in Cretaceous age sandstones and mudstones. These sedimentary rocks were deeply weathered and this weathering released silica into the groundwater. Small faults and joints in the rocks formed pathways for movement of the groundwater as it penetrated downwards.
Impermeable barriers between the sandstone and the underlying rocks trapped the silica-carrying groundwater where it slowly hardened into a gel forming opal in veins and lenses.
Spectacular mineral replacement with opal can also occur. The so called ‘opal pineapples’ found at White Cliffs, NSW are opal pseudomorphs of the mineral Glauberite are examples of this.
[ Excerpt from Geoscience Australia ]
Double Opal Pineapple Pseudomorph