10 January 2011

Mystery rock with radiating crystals

Posted by Callan Bentley

Putting up the wavellite crystals on Saturday reminded me that I needed to show you this thing and ask you to tell me what the hell it is:

I got this from an amateur geologist rockhound dude in Maryland, who got it from a collection of rocks hoarded up by another rockhound. When the one rockhound died, his widow let my rockhound go through the collection and claim whatever he wanted. My rockhound had this piece (bigger then) in his backyard, and then offered it to me. Because I have a rock saw, I suggested that I slice it in half, and we each keep a piece. So that’s what we did. Now here’s the question: what is this, and how did it form?

There’s no fizzing, anywhere. The little orbs are yellow on one side, and orange in the middle, and red on the other side, and everywhere they are surrounded with radiating green crystals that are stockier (non-acicular) than the wavellite in the previous post. These extend a distance, and then the space in between these mineralogical hedgehogs are either tightly clustered, with a gap in between them (as at the bottom), or they are more widely spaced (as at the top), with the intervening space filled with a white/red/pink cryptocrystalline matrix that looks and feels like chert.

What the heck? Tell me what to think of this oddball. Here’s a closer look, with a ruler for scale: