I’m sure that this is a fairly noob question and one I should be able to find the answer for if I had the time and the knowledge on how lasers work. Is the ability to etch stones/gems/crystals a matter of hardness, opacity, color, or level of polish? Or some combination of the above? In preparation I have purchased a Mohs kit to identify the hardness of many of the stone slabs that I have if it is a matter of density. I’m very interested not only on the ability to engrave the stone for the sake of engraving but also as a method for creating complicated patterns to outline for cabochon creation.
Being opague and not reflective to CO2 laser wavelengths is the main factor.
Having a glass temperature in the right range, and not being overly thermally conductive (to allow it to reach high temperatures) are the secondary concerns.
My geology is not sufficient to make sweeping statements. But non-conductive rocks likely will all show at least a little bit of marking from laser being applied.
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Calling @sociogogue, calling @sociogogue. @shaynebradley, are you referring in particular to gemstones, not just any old rocks like limestone, marble and granite?
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After some research, because I have been interested in working with stone myself, here is some information I’ve found…
The more homogeneous and fine-grained the stone, the better the results produced by stone engraving. Stones like Marble, Granite and slate work best due to the color contrast. It appears as though most of the stones react similarly to glass by melting the surface to remove the material so a deep engraving can not be done nor can the stone be cut with the laser.
I did find this link for an 80W laser that has some particularly dense stones listed as viable:
High Precision Gemstone Laser Cutting Machine
I also looked into Diamond Engraving, and that seems to be completely done with Fiber Lasers and not CO2 Lasers.
However, after I get my laser, I do plan on some experiments to add depth to my jewelry designs by engraving the stones. 
I hope this helps.
Edit: Also if this helps, most “river stones” and “pebbles” are either Granite or Quartz. Granite is a 6-7 on the Mohs scale and Quartz is a 7.
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That is a special application, nothing noob about your question.
It’s going to depend on the mineral. I’ve done a lot of cabochon cutting, but no experience with them and a laser.
I would expect softer minerals like turquoise and lapis to etch well because you can actually “burn” them. The effect in general seems to be a “bleaching” of any color in the stone.
I dont know, but there are minerals that may produce undesirable gasses, I would research cupric minerals like malachite for that reason.
I know you want to cut malachite with a lot of water because of the toxicity of the dust. Every time I have cut lapis on my wet grinder I end up with the sulpherous taste of a struck match in my mouth, so I would be cautious regarding your health and the machine’s, however I expect there are few minerals that would be of concern - just err on the side of caution.
The effect I have seen on harder minerals like granite seems to be a minut shattering of the surface from thermal shock. Same effect on glass. Granite for example is a mineral with three main constituents, quartz- the hardest at 7, feldspar at 6-6.5, and hornblende at 5-6. The difference in hardness and thermal characteristics will yield a surface that reflects the differences.
You would want to be cautious with anhydrous minerals like opal that have a water content. Flash that to steam and fracture the stone.
As @jacobturner pointed out, mineral crystals may exhibit differences in reflection/ absorption.
I’ll bet you discover some unique applications in your work!
That link @ray716 provided has some cool examples of different results! There is some inspiration for you!
Thanks ray!
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Thank you for asking this, as I’ve wondered about it too! I’ve been curious about the potential (if any) for basic cabbing and/or surface etching of semiprecious stones.
@ray716 thank you for sharing your research! Sounds like cabbing is unlikely, but engraving might work depending on the material.
My brain has been spinning on all of the possibilities(?) for jewelry design and even just garden art.
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We have a small pet cemetery on the grounds and my father has been bothering my brother (brothering?) for some engraved stone slates to identify the lost pets that are buried there. I guess I’ll be helping my brother a hand come june/july.
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I had inquired early on about creating a memorial marker for my parents grave. I had thought about slate, because it’s so beautiful…and could have been something I could engrave with the Glowrforge. Folks more knowledgeable than myself suggested that slate, over time, could absorb water and would therefore weather faster than something else. I’m thinking now of marking some metal and mounting it on a nice piece of columnar basalt. Whatever the material, it’s a worthy project.
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I think something got lost in translation here. I was not aware slate was a sort of rock/stone. I thought a slate was just a different word for a slab or a ‘thin’ cut of rock/stone. I was planning to use dark Granite for this project and maybe even coating it afterwards with a sealant. Although if the engraving shows for the better part of the decade I’ll be fine with it.
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Slate is a particular from sedimentary stone originally of very fine ash or clay that formed shale, and metamorphosed into slate.
The laser bleaches the color, so a darker slate yields a higher contrast. It tends to cleave along its thin layers, so it often presents an interesting surface texture.
I’m looking forward to working with some!
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I would put it more as a wide range of rocks. I certainly wouldn’t try to do anything with Opal as it fractures when heated, but I have a large range of slabed material that I have been collecting, ranging from opalized petrified wood, obsidian, random material that the wife thought looked nice and at some point would like for me to make drawer pulls out of, etc… So not exclusively gemstones, but I hadn’t even considered limestone as a possibility.
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I can see what you were thinking in terms of definition…and it makes perfect sense. But there really IS a type of stone called slate…as printolaser kindly described.
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Learn something new every day. English is not my native language.
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Wow.
I wish I were educated enough to wield another language as well.
If I may ask, what is your native tongue?
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I’m from the Netherlands so my native language is Dutch. I travel a lot too and pick up a language quite easy when I’m around single language folk. Spanish, French, German even Japanese. But just as easy do they disappear from my head when I’m not using them. I try to remember at least how to order a beer in all the countries I’ve been or passed through!
But we are derailing the thread here. What other uses have laser engraved stones?
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Necro-ing again (sorry, sorry, sorry) because I’m heading to the Tucson gem shows soon, and I’ve been thinking about what types of stones I might grab for experimentation. I usually shop with an eye to unusual beads and cabs for my jewelry designs, but I thought it would be fun to pick up a small variety of polished rock & slab with the 
in mind.
I’m hoping that @printolaser - or anyone else with lapidary skills - might be able to suggest a few gemstones that might be have better odds of being laser-able, as well as any that I should avoid (like the malachite example above).
Thanks in advance for any suggestions!
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Okay, so I don’t yet have a Graduate Gemology degree or anything, but here is what I plan on trying.
First, confirmed laserable materials.
-Slate
-Marble
-Granite
Confirmed NOT able to be lasered with a 
-Diamond
-Corundum (Sapphire and Ruby)
Likely possible candidates:
-Organics: Pearl, Jet, Amber, coral, bone
While I’m sure that these CAN be lasered, I’m not sure what the results will be, nor am I sure how much material will be gone through before acceptable results are achieved. I know that I will be experimenting with these myself…
Semi-Precious:
-Quarts:
While it’s likely these can be engraved with a 40/45w laser I’m not exactly sure what the results will be. That being said, expect Amethyst and Citrine to discolor due to the heat. That is also likely to happen to many of the other varieties of colored quartz.
-Jade:
This is a soft and easy to carve stone that has a very tough crystal matrix. I expect it to react similarly to marble… Same with most stones below Mohs scale of 7.
Now I would be cautious of many gemstones and find out their chemical composition since burning will release that in gaseous form and could be very detrimental. Quick google or wiki searches will give you the chemical composition and help you determine if they are safe or not. I plan on doing a LOT of experimentation in this area after I get my own
Hope this helps!
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It does help, thanks.
And this is an interesting observation:
I figured that quartz, agate and jasper varieties would be an easy go-to (since they’re common and thus, affordable) but I didn’t really think about how the laser might affect color. I know that a lot of smokey quartz is heat treated and/or irradiated in order to darken the color, so it makes sense that this could be a potential side effect.
Thanks for bringing that up. I was mostly concerned with aspects like hardness, reflectivity and chemical compounds, but now there’s yet another variable to consider.
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You should also look for some tagua nuts; they are used as an ivory replacement for scrimshaw and netsuke and such. I’ve seen lots of them at the Tucson show (wish we were going this year) and you can buy them in slices.
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… I’ve shattered and destroyed my share of Amethyst and Citrine during the design process or while I was repairing a ring… so yea…
Anyway… I plan on doing extensive experiments on a few different Quartz varieties… Adding symbols to some of my designs will just increase the depth of awesome if I can do it well enough. And I love experimenting…
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