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Rare Mineral Unearthed in 450 Million-Year-Old Meteorite Impact Crater

Rare Mineral

Image credit: Cheryl Colan, “Meteor Crater” via Flickr. CC BY-NC 2.0

When researchers were exploring an ancient meteorite impact crater in Wisconsin, they found a very unusual mineral which had been discovered three other places before. Such mineral, was known as reidite, a polymorph of the fairly strong gemstone zircon to be generated when the zircon was exposed to quite high pressures. Scientists were able to form this mineral in their laboratory, because it is rare to have the reidite in a natural way.

The researchers made the discovery in Rock Elm, located in western Wisconsin, in the Unites States, which was a 6.5 km diameter impact structure. The crater was formed in the Middle Ordovician period that was from 450 to 470 million years ago, so it should be the oldest discovered reidite so far.

It was suggested that during such period of time, a big meteor shower took place as a result of two huge asteroids that was measured 100 km across at least, and these two slammed into one another between the space of Mars and Jupiter, thus giving off a huge cloud of smaller rock fragments. It would take them a few million years before getting to the Earth. It was surprisingly seen that some were still hitting the Earth for the time being.

It was clear that reidite had been discovered in three other impact craters, such as Chesapeake Bay Crater in Virginia, Ries Crater in Germany and Xiuyan Crater in China, However, Rock Elm was expected to be possibly the last location where scientists were able to identify the mineral. In the interview with Live Science, Aaron Cavosie, geochemist and study author said that no one in their right thinking would have searched for reidite in sandstone.

When meteorites slammed into the ground, zircon would turn into reidite, because remarkable increase in pressure and temperature at the place would be caused by the shock waves from the impact. And the same time, the high pressures would allow the building blocks of the mineral to be rearranged and got repacked very tightly. Although, in the similar composition compared to zircon, the resulting mineral was about 10% more dense than zircon. In addition, reidite could be created in the laboratory experiments in regard to high-pressure or shock recovery. But actually, reidite was the only lab-made samples made just 30 years ago, because it was first found in the natural world in 2001.

The latest samples of reidite were discovered amongst shock-metamorphosed zircons. Such shock metamorphisms would lead to the modifications in rocks and minerals as a result of the passage of shock waves. Based on their initial examination of such samples by the means of microscopy, Cavosie and his team identified the existence of reidite by bombarding them with electrons, because different minerals would diffract electrons in a unique way.

As pressures, namely between 30 to 53 gigapascals, would to morph zircon into reidite, its existence at Rock Elm showed that the meteorite impact would cause much higher pressures than scientists thought before. According to the earlier estimation, the presence of shocked quartz meant that the resulting pressure would not possibly exceed 10 gigapascals. In addition, there should be more reidite to be discovered on Earth than previously expected, because zircon would exist in any crater carved from sandstone,

Source: Live Science

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