Common Opal is a mineraloid that is non crystallising and is classed as an amorphous silicate, the chemical composition for Opal is SiO2 nH2O. Opals can develop in weathered sedimentary rock typical in arid regions where limited water enters small gaps in the rock, and the silicate is hydrated. Common opals, unlike precious opals, do not exhibit ‘play of colour’ in which the colour appears to change depending on the angle of view. While precious opals are highly valuable and cut as gemstones for jewellery, common opals can be cut into inexpensive gemstones and are also mined for various uses including as ingredients in ceramics, insulation, fillers, and abrasives. The source of this common opal specimen is unknown, but common opals are found around the world, notable deposits are found in Queensland, South Australia, New South Wales, Peru, Kenya, Nevada, Oregon, and Mexico. This common opal specimen is of historic and scientific significance due to its donation in 1868 as part of the Geological Survey of Victoria and as a typical example of uncut common opal. This specimen is part of a larger collection of geological and mineral specimens collected from around Australia (and some parts of the world) and donated to the Burke Museum between 1868-1880. A large percentage of these specimens were collected in Victoria as part of the Geological Survey of Victoria that begun in 1852 (in response to the Gold Rush) to study and map the geology of Victoria. Collecting geological specimens was an important part of mapping and understanding the scientific makeup of the earth. Many of these specimens were sent to research and collecting organisations across Australia, including the Burke Museum, to educate and encourage further study.A palm-sized amorphous (non-crystallising) hydrated silicate mineraloid specimen in shades of brown, orange, and white.Existing label: Common Opal / Locality unknowngeological specimen, geology, geology collection, burke museum, beechworth, common opal, opal, mineraloid, amorphous silicates, hydrated silicate