Technically, Darwin Glass is not a mineral – but a frothy, pale-green-to-black siliceous glass known as ‘impactite’, which was formed when a meteorite struck Tasmania and vaporised rocks and soil, some 750,000 years ago. The impact site (called an ‘astrobleme’) is the Darwin Crater, found east of Mount Darwin, 20 km south-south-east of Queenstown – yet no Darwin Glass can be found within this weathered structure.

Darwin Glass is found in small amounts on the eastern slopes of Mount Darwin, the shores of Lake Burbury, on the eastern slopes of Ten Mile Hill, and many other areas. It is usually very irregular, slaggy, with twisted stalactitic forms and with rare teardrop and disc-like shapes. Numerous bubble pits are present and the pieces are consequently of very low density and have a contorted appearance – described by early prospectors as “petrified kelp”.

Darwin Glass is closely related to ‘tektites’ – droplets that were blasted high into the atmosphere by the initial impact. (Another variety, called ‘australites’, is widespread on the mainland and may have resulted from an impact in Indochina.)

Darwin Glass is also known to have been used by Tasmanian Aboriginal people for the production of stone tools as it flakes well, creating extremely sharp edges. Darwin Glass tools have been found in locations around Tasmania, including in the Macquarie Harbour region and at Kuti kina Cave on the Franklin River, where its use dates back from 20,000 to 15,000 years ago. Its most easterly distribution is at Nunamira Cave near Mount Field, where the oldest Darwin Glass stone tool found dates from 27,000 years ago. Its northern-most distribution is approximately 170 km north of the original impact, at Mackintosh Cave – and this distribution from the source site suggests long-distance transport and exchange networks between Tasmanian Aboriginal peoples.