New answers tagged rocks
7
These are most likely manganese dendrites. It is not a fossil, and not organic. These usually form in cracks in rocks, and most likely this slab was broken along an existing crack.
You can read more about it now: https://www.mindat.org/min-26645.html
One comment: this is not basalt. Basalt is black. Most likely some form of limestone.
1
They are quite pretty, but they are not fossils. They remind me of the patterns that frost sometimes makes on window panes. A similar process is at work here, though with mineral bearing water infiltration rather than frost being the cause. The water infiltration deposits crystals in the rock.
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