This week's theme was: D is for Distorted
The thing about being married to a geologist is that you end up with lots of rock specimens around the place. In this one you can see the tiny fold where the rock has been distorted by heat and pressure.
I'm afraid I don't know what the rock is. If I can catch G in a non-stressed moment, I will try to remember to ask, but for the moment it will just have to be Unidentified Interesting Rock.