20 February 2012

Mystery rock

Posted by Callan Bentley

Here’s a mystery rock that’s just aching to have its identity be crowdsourced:

I got these photos from Rick Diecchio of George Mason Univerisity, who got them from a local fellow who dug it up in his yard in Dale City, Virginia. Rick says:

I was stumped at first, but the more I look at it, the more I think it’s a lightning strike into sand or more likely sandstone, maybe the Cretaceous Potomac Formation.

The host rock is all sandstone. The sand appears under hand lens to be fused, and on the surface there is a chert-like coating which I think may have been the result of melting. The sample is a lot heavier than I would expect, and very well indurated.

What do you think? Are there other options? Have you ever seen anything like this? If it is a fulgurite, how common or rare is a sample this size? Feel free to share these pics with others who may be interested or who may be able to provide information.

A silcrete concretion is possible. Then it becomes significant whether or not the sand grains are fused. maybe will have to get a thin-section. There is no sign if anything fozzilized. No bone or petrified wood as far as I can tell. The size is the biggest problem for me. Most fulgurites I have seen are an order of magnitude smaller.

Any ideas, wise readers?