Simple Specimen with an Unusual Dendrite Structure

I spent about an hour trying to get a close-up image of an odd structure inside this thunderegg. And ... can't say I really succeeded. I think I would need better gear to really take a close look at this. This isn't a crack - at least not any normal kind of crack. It's a fuzzy line in the agate that has no effect on the polished surface, surrounded by dendrites. Never seen anything quite like it before! One day I really have to buy a digital microscope!

7.5cm