Rare moon rock samples found in Australia
The last of the three minerals brought as rock samples from the moon and believed to be uniquely lunar – tranquillityite – has been found on earth.
Scientists in Australia discovered the mineral, which was named after the Sea of Tranquillity, in rocks at six sites scattered across the west of the country. Two other minerals, armalcolite and pyroxferroite, were found on earth within a decade of the moon landing.
The mineral tranquillityite occurs only in small amounts and has little known use aside from dating the rocks in which it is found. It had previously been found only in lunar rocks and meteorites.
An Australian palaeontologist, Birger Rasmussen, from Curtin University, said he was surprised that it had taken more than 40 years to find tranquillityite on earth, especially as its chemistry is not particularly unusual.
"This was essentially the last mineral which was sort of uniquely lunar that had been found in the 70s from these samples returned from the Apollo mission," he told Fairfax media.
"We had been studying lunar rocks previously, so we'd come across tranquillityite in rocks from the moon. So we knew roughly what to look for and then we happened to be looking at similar types of rocks on Earth and we thought 'this mineral should be present, we haven't seen it – I wonder why not? We'll keep an eye out' and eventually we found it." The six American Apollo missions brought back about 842 pounds of lunar rocks, core samples, pebbles, sand and dust between 1969 and 1972. The samples are held by NASA and distributed for scientific research.
Traces of tranquillityite are typically tiny – about 150 micrometers long, or less than the diameter of the thickest human hair. It is reddish-brown and mostly consists of iron, silicon, oxygen, zirconium, titanium and the rare earth element, yttrium.
In an article in Geology titled "Tranquillityite: The last lunar mineral comes down to Earth", Professor Rasmussen and his colleagues report that the substance was found in six dikes and sills in Western Australia.
"Examination of dolerite from Western Australia suggests that tranquillityite is a relatively widespread, albeit volumetrically minor, accessory mineral," they write.
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