Here is a YouTube video that I saw a while ago. https://www.youtube.com/watch?v=kcjfPrmwQX4&t=3s
It shows brick pavers being sand blasted and then painted. This might work for you. 
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Gal knows more about sandblasting, and has a better shop space, than I do.
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I thought we saw a rock of Dan’s that shows a melted surface?
You can do stone - not a very deep engrave but will mark it. I’ve purchased those black “river rocks” at the dollar store and engraved with my K40 ( tube went out after less than 20 hours of use 
) but you can engrave a “white” image that is (seems) permanant.
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To be fair I live on the east coast of Canada and it was in the 20s (Celsius) this weekend. Seeing snow this late is so weird.
I’ve seen snow falling this late in the year, and not that many years ago. I happen to live in Michigan.
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My wife reminded me that the last frost day is around Mother’s Day for Fort Collins.
She has a bunch of plants (that our youngest son gets for her every Mother’s Day) waiting to be planted in her garden areas.
A few years ago we had an Easter Snow in North Texas. So basically, anything is possible 
Ummm… I think that’s called Colorado now.
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I finally remembered to photograph my river rock vs Hobby Lobby stone comparison…
Multiple passes at 30 and 50% power:
Gneiss, but not quite what I wanted…
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I’m not that old 
, I just look like it (I went gray early). No, this was south of Fort Worth about 30 miles.
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Lighter one looks:
- More natural.
- Like it reflected more of the light.
- Like it has a more varied composition.
Did you try overlaying the same engrave on it a second time without opening the lid? (Just rerun the laser/project?
The darker one looks almost like it had a false finish that you were burning off.
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It actually does make sense that a lighter stone may reflect more and engrave less.
Yes, both were engraved multiple times at 30 to 50% power w/o opening the lid. I also ran a cut/score around the letters since the text were vectors.
Curiouser and curiouser.
@dwardio There are lots of different kinds of “rocks”. Those two may have entirely different chemistries and I am not surprised they lasered so differently. Around here, for instance, the beaches and rivers are filled with the result of glacial activity, which means the rocks can come from almost anywhere. I regularly find white quartzite next to sandstone next to basalt. When it comes to lasering pebbles, you can’'t take anything for granite.
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Are you a geologist Josh? (Dang! Missed the pun…excellent!) 
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Agreed – we have the same sort of mix here (a stone’s throw from GSA HQ). I knew there would be a difference, just like different spp of wood. This was just a grab-n-go test.
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Stretch marks! 
No, but I like rocks (and puns). 
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