Billion-year-old rocks in the Australian desert have yielded a rare mineral previously thought to only exist on the Moon or in lunar meteor samples that have crash-landed here. Its discovery here on Earth is expected to help scientists better understand the history and geology of the Earth and the moon — which may not be so different after all.
Tranquillityite is a mineral consisting of iron, zirconium, yttrium, titanium, silicon and oxygen. It is named after the moon's Sea of Tranquility, where it was first discovered by Apollo 11. The terrestrial version, located in six remote sites, occurs as in strips about the width of a human hair and only microns in length that likely intruded as magma into the surrounding stone.
So why has this rare mineral remained hidden for so long? Birger Rasmussen, a geologist at Curtin University in Bentley, Australia made the discovery. He says, "Tranquillityite was probably not found until now because it is relatively rare and small. [It] is also prone to alteration during later heating and fluid flow."
Standard techniques that were used to analyze the ancient dolerite rocks found to contain the mineral usually involved crushing the rock — a process that could have destroyed the fine samples. Rasmussen and his team only found the samples by investigating polished slices of dolerite under scanning electron microscopes.
Additionally, the tranquillityite erodes at a rapid pace when exposed to natural environmental conditions and may have just slipped through the hands of scientists previously studying the rocks. Another theory is that the mineral can only form through a unique set of circumstances — involving uranium decay.
In a word, tranquillityite is elusive.
That said, Rasmussen notes, "I think we will find that it is much more widespread on Earth — there is no reason that it should be restricted to Western Australia,"
The find is an exciting one in helping scientists understand the geology of both the moon and the Earth. Because the tranquillityite has a set of properties that make it good for using the uranium-lead method of estimating the age of rocks they could establish the volcanic rocks in northwestern Australia were about one billion years old — much older than previously thought.
It's also evidence the minerals were likely always located here and tantalizing proof that the Earth and the moon likely shared the same chemical processes at some point.
The scientists detailed their findings in the January issue of the journal Geology.