8 March 2010

Suevite from Vrederfort

Posted by Callan

One of my students brought this sample in the other day:

She said her father collected it in South Africa. It was labeled “suevite.” I learned the term suevite about a year ago, while touring the USGS Chesapeake Bay Impact Crater coring project samples at the USGS Headquarters in Reston, Virginia. Wright Horton taught me that suevite is impact-generated melt that chills with other chunks of the pre-impact rock mixed into it. Sometimes, it is glassy. There was a bunch of it deep in the Chesapeake Bay Impact Crater core.

So I put this together in my head and asked “Where in South Africa did this come from?” The student couldn’t remember, but it was “some weird name.” “Was it the Vrederfort Structure?” I asked? Her eyes lit up: “Yes! That’s it! How did you know?” I didn’t know: but that’s the only impact site in South Africa I could name offhand. So I think that’s what this is. A pre-Vrederfort Impact granite smashed and melted during the impact, with individual mineral grains breaking off and mixing into the melt, which then solidified into suevite. Pretty neat little sample! I’d love to have one of my own, but settled for making a digital scan of hers. E-mail me if you want a bigger copy.