What are australites?
Australites are a variety of mysterious dark glassy fragments known as tektites. These are pieces of rock which have been completely melted as they descended at high speed through the Earth’s atmosphere. There are four main regions on Earth where tektites have been found scattered on the surface. Tektites from each region, or strewnfield, have a distinct age. The youngest tektites are those found across much of the southern two-thirds of the Australian continent. Australites, as these are called, show a wide variety of regular shapes that have resulted from aerodynamic sculpturing of the molten glass during their descent. Australites from western Victoria, in particular from the Port Campbell district, are the best preserved. They are typified by round buttons up to several centimetres across, each with a delicate flange around the girdle.
How did they form?
Australites have been known to European scientists since the 1830s, however Aboriginal people used them as sacred objects or as cutting tools. There have been many different theories on how australites formed, including production by bush fires, eruption from volcanoes or fusion of dust by lightning. For a time they were thought to have come from the Moon. However, scientists now know that lunar rocks do not have the same composition as australites, and their source is now believed to be Earth itself. They probably originated during gigantic meteorite or comet impacts, when myriads of small rock fragments were blasted into the upper atmosphere, from where they descended to the surface. There are possible impact sites preserved in south-eastern Asia.
Typical australite button with flange from Port Campbell, Victoria (2 cm across).
Photographer: Dermot Henry. Source: Museum Victoria
How old are australites?
The first attempts to calculate the age of australites used carbon dating, not on the glassy objects themselves, but on pieces of charcoal found in the same sandy layers. These methods gave ages of only a few tens of thousands of years. A direct method of dating australites was developed in the 1960s. Known as fission track dating, this technique showed australites are nearly 800 000 years old. Modern geological mapping has confirmed this age is correct.
Why are they important?
Because australites were believed to come from Space, the National Aeronautical and Space Administration of the USA (NASA) was especially interested in them for the Apollo Moon missions in the 1960s. The aerodynamic shape of the perfect flanged buttons were similar to models of re-entry modules. As well, the glass has a composition that provides great resistance to thermodynamic shock and was therefore considered excellent for use as heat shields in artificial satellites and ballistic missiles. NASA even made synthetic australites in special heated chambers. Today, australites are a reminder of the history of large extraterrestrial impacts on Earth.
It is possible to find australites in sandy country across southern Australia, but the rugged cliff tops east of Port Campbell in Victoria provide the best opportunities. Here, they can be found as black glassy fragments in the surface sand, especially after heavy rain. Care is needed however, as these cliff tops are dangerous places. Australites can be collected and owned, but they are protected from export without a permit by Federal legislation.
Museum Victoria has a very good collection of australites, showing all the known varieties. Many were collected by a world famous expert on australites, Dr George Baker, who provided advice to NASA on their properties and occurrences.
McNamara, K. and Bevan, A. 2001. Tektites. Western Australian Museum.
McCall, J. 2001. Tektites in the geological record. Geological Society of London.