Phys.Org has a story about the discovery of one of the Earth's rarest minerals. The mineral reidite was found in samples from an impact site in Rock Elm, Wisconsin. Rock Elm is just the fourth site on Earth where the mineral has been found. The Rock Elm structure dates to the Middle Ordovician, about 450 million year ago.
Aaron Cavosie of the University of Puerto Rico, and member of the NASA Astrobiology Institute Team at the University of Wisconsin, brought students to an impact site in Rock Elm, Wisconsin to collect samples. In those samples, Cavosie and colleagues discovered the mineral reidite, making Rock Elm the fourth site on Earth where the mineral has been found in nature.
Reidite is created at high pressures and was first identified in the laboratory in the 1960s. The conditions in which reidite forms have been well-constrained by experiments in the lab but, prior to Rock Elm, it was only found naturally in the Chesapeake Bay Impact Structure (Virginia), the Ries Crater (Germany), and the Xiuyan Crater (China).
The Rock Elm structure is 6.5 kilometers in diameter and was formed during the Middle Ordovician. This means that the reidite found at Rock Elm is at least 450 million years old, making it the oldest preserved reidite yet discovered.
More information: The initial findings were presented at the 2014 GSA Annual Meeting in Vancouver: gsa.confex.com/gsa/2014AM/fina… /abstract_244685.htm
Read more at: http://phys.org/news/2015-01-rare-mineral-wisconsin-crater.html#jCp