Moses would think twice before smashing those up Jim, well done!
You should experiment with stone and your laser. Fine-grain rocks can be etched and if you paint them first with grade school tempura paints, you can etch in colors. White paint contains titanium dioxide which melts into a deep black and fuses to the surface. If you play with adding mica powder you can skew the tint.
Slate is a common material people etch for coasters, etc.