http://www.abc.net.au/science/news/stories/s997056.htm
Meteorite impact creates new mineral Heather Catchpole ABC Science Online (Australia) November 26, 2003 A new mineral made by a meteorite smashing into the Earth has been found by Chinese researchers. They said their discovery of a new form of chromite could teach scientists more about the strength of meteorite impacts and how deep in the Earth minerals are born. Researchers led by Ming Chen of the Chinese Academy of Sciences published details of the new mineral, which was formed at high pressure and temperature, in this week's issue of the Proceedings of the National Academy of Sciences. The new form of chromite is an ore of the metal chromium, which is found at meteorite impact sites as well as deep in the Earth's mantle, the layer of rock that sits directly below the Earth's crust. The researchers found the new mineral in shock veins formed by the impact of the Suizhou meteorite on China in 1986. The shock of the impact created temperatures of about 2000°C and pressures like those at 600 kilometres below the Earth. The researchers also made a version of the new mineral in the lab. They did this by using a laser to subject the mineral to intense heat while squashing it under a diamond anvil. Researcher Professor Hugh O'Neill of the Research School of Earth Sciences at the Australian National University in Canberra, said the new find was interesting. "This potentially gives us clues to the orbital velocities of two bodies that come together to produce these shock collisions." The researchers calibrated how the crystal form of chromite changed with increasing pressure, to create a kind of Earth-based barometer or pressure gauge. They said this could be used not only to gauge the strength of meteorite impacts, but also to gauge the pressure at which rocks formed over an important range throughout the Earth's mantle. But O'Neill, whose team has synthesised a different, more magnesium-rich version of chromite, doubted the calibrations could provide a comprehensive depth gauge for rocks, saying that this was maybe "stretching the results a little too far". "At depths equivalent to the pressures they are talking about you don't find this mineral. It reacts to form garnet," O'Neill told ABC Science Online. Chromite is normally only found at depths of about 80 kilometres below the Earth's surface, where pressure is far less than the intense pressure created by meteorite impacts. And under the shock conditions of a meteorite impact pressure is applied and released quickly, whereas in the Earth chromite is under continuous pressure for millions of years, O'Neill said. Under natural conditions chromite was likely to react with other minerals, like magnesium and iron, to form a new mineral, he said. Despite this qualification, O'Neill called the find "rare", and said that the researchers would have the chance to name the new mineral. ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
