The stone is kind of soft, it has a clay like feel to it.
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Its colored like a Thuringian.
+1 on the CA. Better compression more even bond line. Gorilla glue can expand. 2 part epoxy can too if you whip enough air into it. Then you get bubbles which are weak spots. There are many choices, Loctite should have a iso-cyanate version that would work well enough too.
All of these are brittle when cured so be careful Oh, looks like an Escher to me. I always try to keep my stones over some kind of padding when working with them. Oh well it happens. It's only a stone, maybe a better one will come along.
Mike:)