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PUR adhesives are safe when cured, but can cause allergic reaction and irritation on use.
In some cases it can cause isocyanate sensitization (chemical asthma).

Here it is MSDS for example:...

this is a kind of polyurethane adhesive like Gorilla Glue, Kleiberit Pur ADHESIVE 501, Titebond #2300 Polyurethane Glue, etc.
all of them contain isocyanates that are not safe for health.

Once you put the stone on the epoxy you have a little chance to unglue it.
It is too hard to be easily removed with knife or chisel.
The decomposition temperature of epoxy is about 450С ( 850 F)....