Experimental fun, robing nature of its work in some way, cast concrete in what it seems to be... a stone... but it is not. It is concrete sealed with concrete paint and concrete sealer and set into a copper form as would be any gemstone.
The fun part is the tale to tell, how when somebody asks which stone it is you can brag about concrete. ;)
It measures total 64 x 21 x 7mm approx.