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A slice of the dolerite found to contain tranquillityite from the Pilbara region of WA. (Credit: Birger Rasmussen)

Moon mineral found in Western Australia

  • BY Natalie Muller |
  • January 17, 2012

A rare mineral thought to exist only on the Moon’s surface has been discovered in WA's Pilbara.

RESEARCHERS COLLECTING ROCK samples in Western Australia's remote Pilbara region have stumbled across a mineral previously believed to exist only on the Moon.

The team from the University of Western Australia (UWA) and Curtin University in Perth say they've found 'tranquillityite' in dolerite rocks at six different sites in the state's north. In the current issue of the scientific journal Geology, they explain the red-brown coloured mineral could be used as a handy new tool to date rocks more accurately.

Named after the Moon's Sea of Tranquility where Apollo 11 landed in 1969, tranquillityite was first identified in the 1970s in rocks Neil Armstrong's crew brought back to earth. Scientists poring over these lunar samples also found armalcolite and pyroxferroite, two other substances once believed to be unique to the Moon. But while both minerals were discovered on Earth over 30 years ago, tranquillityite remained a mystery.

Confirming the mineral identity

"It was unusual tranquillityite hadn't been found in terrestrial rocks until now," says Dr Janet Muhling, a geologist at UWA who helped confirm the mineral's identity. "I think if the earthly rocks had been looked at with the same level of detail as the lunar rocks [since 1969] then perhaps it would have been found earlier," she says. "We suspect it will probably be found in a number of locations if people look for it."

At the UWA's Centre for Microscopy, Characterisation and Analysis, Janet analysed the newly discovered mineral beneath an electron microscope to make sure it shared the same composition and crystal structure as lunar tranquillityite. By targeting the grains with an electron beam, and examining at the X-rays emitted, she could see which elements were present.

Tranquillityite appears as miniscule crystals, and is mostly made up of silicon, zirconium, iron, oxygen, and titanium. It also has a small amount of uranium, which is one of the most effective components in helping to estimate the age of rocks and other minerals associated with it.

 
The mineral tranquillityite was discovered during Neil Armstrong and Buzz Aldrin's moon landing in 1969. (Credit: NASA)

Dating rocks

The research team used uranium-lead dating to show the Pilbara rocks containing tranquillityite were over 1 billion years old, about 200 million years older than other scientific estimates. "So it was older than had been thought from the previous mapping in the area," says Janet.

"Obviously the age of the rocks also has a bearing on mineralisation and just working out the geology - whether an area is going to be prospective for certain sorts of mineral deposits or not - so it's quite important to work out the ages of the rocks."

Janet says it's likely tranquillityite is quite widespread, but more research is needed to find out just how common it is.

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