Does anyone has engrave on rocks or stones? This may sound a little bit crazy, but, Is it possible? What type of laser would I need?
I’ve tried on glazed & unglazed tiles. Worked okay, but not very deep. Although I had the power at about 10mA when I tested. Not sure if we could do it on rocks, but would be interesting to test & see. I think some people here have engraved on slate if I remember right.
I just posted a photo of my test runs doing rocks. Same as glass. Wet paper or dish detergent prevents chipping. During my tests I had a rock explode when I tried to drill a hole
It does work. Higher power is better. Similar to glass in fact. Different rocks yield different results so practice. Also you have to be careful with head clearance and alignment so a projection doesn’t whack the laser head as it travels. Flat rocks are better 
You can also try one of the Theramark/Cermark products. That’s a solution you paint on the surface and then etch (really it just “marks”). The paint then fuses to the surface and you can wash off the rest. Works kind of like toner in a laser printer.
@Jim_Hatch Thanks for those suggestions/advice Jim.
I find slate great to work with. Cheap and looks great.