This is a slice of a thunder egg. The back light had to be strong for the details in the darker parts of the rock to show. Thanks for the feedback I have an idea that pure abstracts don't do well here.
I think I should have pushed the curve a little more like this.
What is it? I find it hard to give a good score to something I can't figure out. A lava flow? The inside of a geode? Some strange space cloud? I'm baffled, just don't know what I'm looking at.