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CrustalTrudger t1_j683w0w wrote

Fun idea, but minerals don't work like that. First, some basic mineralogy stuff. Amethyst is just dirty quartz and sapphire is just dirty corundum, i.e., amethyst is a quartz crystal that has impurities (usually iron, but sometimes other metals) and sapphire is a corundum crystal that has impurities (for a blue sapphire, typically iron and titanium). For reference, there are other color sapphires (with different elements subbing into the crystal lattice, producing different colors) and we give other names to corundum with different impurities (e.g., if corundum has chromium in it, it will tend to have a red color, which we call a ruby).

So lets say you take some amethyst (quartz - SiO2 - with some Fe) and sapphire (corundum - Al2O3 - with some Fe and Ti) and put them into a crucible, how hot would you need to get them to melt? Well, quartz (for a rock forming mineral) melts at relatively low temperature of around ~570 C (assuming we're basically doing this at atmospheric pressures) EDIT depending on the type of quartz and the duration of heating, will melt at ~1750 C (e.g., Folstad et al., 2023), but we need to get our mixture up to ~2000 C to melt corundum. Let's say you have the right equipment to do that and you get both your amethyst and corundum into a melt, you've basically made a "melt" consisting of Si, Al, O, Fe, and Ti (assuming that the amethyst was an amethyst because of Fe and not some other metal).

If you start cooling this melt, what's going to happen? Well, you'll start to crystallize things, and effectively you'll crystallize things in the reverse order. I.e., whatever melted first EDIT: last - will start to crystallize first. So in a super simple scenario, as the temperature of our mixture drops below ~2000 C, you might start to get bits of sapphire to crystallize. This is effectively a reflection of one of the basic things we teach in an intro geology class, i.e., Bowen's reaction series, which basically is a progression of minerals you'd expect to crystallize out of a melt containing a mixture of common mineral forming elements (or in reverse, what order you'd expect minerals within a rock to melt as you ramp up the temperature). This progression effectively relates back to the melting/crystallization temperature of different minerals, but also the evolution of a melt, i.e., when a particular mineral crystallizes from a cooling melt because it is thermodynamically favorable to do so, depending on what constituents it "takes up", the composition of the melt will change.

With that in mind, and returning to our specific example, importantly, you've got a melt that has some extra components compared to your original sapphire, namely Si, so chances are you might not even get sapphire (or corundum) back, for example, you might start to instead crystallize an aluminosilicate, i.e., Al2SiO5, specifically probably andalusite since we're doing this experiment at atmospheric pressures) or some other minerals depending on the exact mixtures and conditions as you reduced the temperature. As you continue to cool the melt, finally, you'd probably get quartz, basically using up what ever Si and O were left. Whether this quartz looked anything like amethyst would depend on whether the minerals that crytallized before it had left any iron around. Effectively, what you've done is made an artificial rock, i.e., a mixture of one or more minerals but where the individual minerals are distinct crystals. Also of note, it tends to take relatively specific conditions to grow large crystals that we could consider "gem quality", and chances are, our experiment would not result in this, but instead a relatively fine grained rock with lots of little crystals, so probably not a very pretty rock.

You also might be asking, instead of cooling our melt slowly and letting crystals form, what if we cooled it really quickly, i.e., if we "quenched" our melt? Well, then you've basically formed glass. Chances are it's going to look basically like obsidian, which is a natural form of glass from rapid cooling of melts rich in silicon, oxygen, and aluminum (along with some other bits) kind of like our melt.

Finally, it's worth noting that the material properties for minerals and metals tend to be very different. Those differences in material properties allow metals to be "worked", i.e., you can deform them in a "ductile" manner even at low temperature and pressure to form things like rings. At atmospheric temperatures and pressures, most naturally occurring minerals instead deform "brittlely", i.e., they fracture. So, you would not really be able to form a mineral into something like a band, unless you had a single crystal large enough to just cut a ring shaped object out of this crystal. You can get minerals to deform in a ductile manner, but it takes relatively intense temperature and pressure conditions to do so and not exactly something you can do in your kitchen, unless for some reason you have a diamond anvil cell in your kitchen.

EDIT: For all the people asking me various forms of, "what if you did this other kind of manufacturing technique on minerals/resin/other stuff to get the desired effect?" this is a fundamentally different question than "can you melt two minerals together." The former question is relevant for what OP wants, but is not really for a geologist to answer (i.e., most of us are not professional jewelers, oddly enough). I.e., stop asking me how to make jewellery, I don't know how to make jewellery.

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garyisaunicorn t1_j689b2m wrote

Take my pauper's award for such an interesting and comprehensive answer! 🏅

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JohnGenericDoe t1_j68oehe wrote

This dude always comes thru with expert and detailed information - with sources.

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-Metacelsus- t1_j68m3ac wrote

> whatever melted first will start to crystallize first.

wait, don't you mean whatever melted last (i.e. has higher melting temperature) will crystallize first?

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s00perguy t1_j68i3y9 wrote

Oh sweet Jesus that's some good sourcing.

Hey,while it isn't quite like mixing dyes and creating a gradient, you could grind the gemstones in question and create a resin suspension for a similar effect, assuming none of them react in any way with standard 2 part epoxy. You could grind them fine, mix them into their respective resins, mix them, and let it cure.

Or, if you're more concerned about carrying over the crystal structure of the original stones than getting a strictly smooth gradient, you could polish them to a uniform shape and bond them somehow. Suspending in epoxy is still an option for that.

Just some ideas, idk if that works on all fronts.

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LittleCreepy_ t1_j6anu54 wrote

Would that even work? Gems generaly produce a different colour powder than what we see from a single crystal. Could potentially ruin your gem.

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s00perguy t1_j6aqkqv wrote

For one, you can buy gem powder directly, and it's incredibly cheap, and you'll notice I mentioned a method for using contiguous gems later in the thread

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emptybottleofdoom t1_j6955oe wrote

Sounds expensive but possible? Lab grown gems, with resin suspension of the two gems, ground up, in a gradient from one to the other?

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s00perguy t1_j698f68 wrote

I mean, it was going to be expensive anyway. It's also not hard to find just gem powder now that I'm thinking about it, because people want big, contiguous gems. So finding a whole or many to make up or encrust a full wedding band? Incredibly expensive. Loading gem powder instead of a dye into resin? Not cheap, but moreso, and less of an artistic statement imho. If you want plain colored crushed crystal, glass/cubic zirconium is an ideal stand in. Like, you can make that idea for relatively cheap, set it in a band of a nice gold/silver, and it would look just as good, because you obviously lose some of the qualities that makes gems desireable in the first place, if the fact they're your birthstones don't really matter. But if you have multiple whole gems to really fill out the band, and the money to really splash out in the jeweler, it could be gorgeous.

So basically, as always, it comes down to what exactly you want, your budget, and how much appearance matters next to what the materials actually are.

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emptybottleofdoom t1_j698uff wrote

We kinda went from "how minerals work under heat" to debating jewelry, huh.

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s00perguy t1_j6993lq wrote

Eh, it'sdirectly related to the main post. Also I have been thinking in a crafts headspace for a few days while working on my most recent post.

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kcasper t1_j6bbm44 wrote

>Loading gem powder instead of a dye into resin? Not cheap

The only really expensive part here is acquiring the gem powder. The rest is pouring it in a mold, letting it cure, and then polishing it into a specific detail. Simple round rings are terribly easy to make. Longevity is an issue as you need to know the correct formula to keep the outer layer from flaking or peeling apart.

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Sevulturus t1_j69i2c3 wrote

Lots of people are doing something close when making bent wood rings. This one for example uses crushed turquoise, but grinding it finer and then laying out a gradient likely wouldn't be that tough.

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lezzerlee t1_j6ab0bf wrote

I would be worried about longevity of resin compared to a quality metal or harder stone, personally.

ETA resin is soft (relatively) & can discolor after time, especially with exposure to sunlight.

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torama t1_j68ce7b wrote

Nice explanation. The melting point of quartz is wrong though. I used quartz reactors at above 800 C degrees.

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OrbitalPete t1_j6m0dr1 wrote

OK, so forgive my lack of mineralogy but why does quartz only start dumping out of silicate melt below about 800 degrees? Is this at STP?

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torama t1_j6m5nro wrote

Sorry English is not my first language, what do you mean by "dumping out of silicate melt below"?

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OrbitalPete t1_j6m8ett wrote

You only start crystallising quartz in a silicate melt (I.e. magma) below about 800 degrees. Above that the silica only gets accommodated in other minerals.

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torama t1_j6msxjm wrote

Solubility of phases and their precipitation is not really related to their melitng points. Things can dissolve or precipitate at wildly different temeperatures.

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chez-linda t1_j6944h1 wrote

I just spent 30 minutes going through the Wikipedia pages of gems and crystal structures. Incredibly fascinating stuff. This makes me want to take a class in geology next year, so thank you

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CrustalTrudger t1_j696e59 wrote

I am of course incredibly biased as a professional geologist who teaches geology for a living, but I would highly recommend an intro geology class for anyone. Developing a basic understanding of the history and workings of the planet on which we all live has intrinsic value and you'll be surprised how relevant much of the insight gained from an intro class will be for random things in your life (e.g., thinking about where to buy a home, etc.).

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pedanticheron t1_j69gjrv wrote

I took some geology classes in college, but it was back when I still believed in the young earth indoctrination of my childhood. After leaving all that about a decade ago, I began studying on my own and was really frustrated with my younger self. My favorite thing I recently found was that my state, Florida, was on two separate tectonic plates.

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CyberneticPanda t1_j68vu8d wrote

Most gem quality rubies and sapphires come from metamorphic rock with igneous intrusions, so you would be real unlikely to be able to get big clean crystals this way. On top of that, you can't really get them out of the metamorphic rock really because you'll break them with the surrounding rock. We mostly get them from sedimentary deposits (placer deposits) when the softer rock around them weathers away and the hard gemstones get picked up by water and moved downstream.

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hifructosetrashjuice t1_j68tu4l wrote

what about growing single crystal of quartz with one dopant, and then grafting quartz with another dopant on it

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RigbyRoadIce t1_j69ar24 wrote

Do you think you could get the "effect" that OP wants by properly cutting two different types of stones to appear to fit together like they're one?

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LittleCreepy_ t1_j6aor09 wrote

One stone beginning thin where the other will be thick and slowly reversing that until we get to a single material. Could work if both gems are really clear?

Probably better than my idea of cutting the high temperature gem into a halve band and encasing it in the lower melting one. Then you only have to cut a ring from that stone. I dont know if you can make a gradient that way tho.

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ArmoredHeart t1_j6auphx wrote

Would you happen to be knowledgeable about the mechanics of the mineral solids? I was wondering how structurally sound a ring cast or carved from a single mineral (let’s say a quartz) would be.

I only ever did a bachelor’s in Geo and do some jeweling and gem-dealing, so I have an educated guess that it wouldn’t be, due to cleavage planes making it brittle. I’m contrasting it with its chemical twin, glass, which is successfully formed into a variety of shapes—I imagine this because of its vitreous crystal form giving it more flex than minerals with actual geometric crystal forms. I was fairly confident at first, then started considering how fast cooling can mean only tiny crystals get to form, so maybe that would be sound compared to carving a ring out of a gem-quality sample.

I also recalled that jade minerals have been carved by humans for ages without casting or modern tools, so now I’m doubting my guess, or wondering if less-than-gem-quality materials would work better.

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girnigoe t1_j6bdafy wrote

I wanted to say something similar but wondered… COULD you actually do a corundum-to-blue-sapphire or quartz-to-amethyst gradient, by growing the gem in a lab & gradually adding the doping (“dirty”) element?

I see your edit & yeah this isn’t melting, but does OP really care about the specific process!?

and a lab-grown gem would still be…clear & sparkly like a gemstone. the resin suggestions kill the whole thing imo

edit: similar to u/highfructosetrashjuice’s comment in the thread.

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SkriVanTek t1_j68e9jp wrote

what about melting the gem stones locally so it is molten only in part and then fusing them together

like a weld. when we want to combine pieces of metal we wouldn’t completely melt them for example

or melting them just above their respective rating points so they still have a high viscosity, limiting diffusion of the individual component elements into each other

or rephrased

what about a process where the components are not in a thermodynamic or kinetic equilibrium?

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Garbleshift t1_j68j5h7 wrote

The description above still applies to the parts you melt.

The point is that when you heat a rock and then cool it, in different circumstances from those in which it was originally formed, you're making a different kind of rock, with different physical properties. Every atmospheric oxygen and moisture are an issue. And minerals haven't been refined the way industrial metals have, so you don't even really know exactly what you're heating up. The chance of the molten part staying stuck to the part that didn't melt is pretty slim.

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julie78787 t1_j68gm4d wrote

You'd likely start getting into issues with the coefficients of thermal expansion being different, as well as thermal conductivity preventing this from happening locally.

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TetraThiaFulvalene t1_j695a5f wrote

You could maybe do it with gemstones that are based on the same mineral with different dopants.

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LittleCreepy_ t1_j6ap4xg wrote

About the only way I see the gradient forming. Sadly that would mean we couldnt use the birthdaystones, as it would be a single material.

Maybe use a stone assosiated with the day the ring will be gifted, so a stone can be chosen that has the right properties for the colours.

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cville-z t1_j68kqeo wrote

Is the chemistry different if you melt them in a reduction chamber, for example a gas-fired kiln, and cool in an absence of oxygen? Or does the O “stick around” because it’s bonded to Si or Al?

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QuitBeingALilBitch t1_j698bjw wrote

What if you took two large gemstones, let's say a sapphire and an Amethyst. Shaved a flat side onto each, then instead of melting the whole thing, you very quickly applied a massive amount of heat only to the flat side. Then as soon as the edge begins to melt, you stick the two flat sides together and let them glue together. The seam probably wouldn't be a pretty gradient like OP wanted, but it might still work? Idk.

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muskytortoise t1_j699ynh wrote

Sapphire melts in 2053°C, amethyst melts in 1650°C. That's problem number one.

Problem number two is: gems are only gems if they form large and relatively uniform crystalline structure while cooling down.^(*some exceptions apply but are not relevant) Otherwise they will look like obsidian, or rock depending on what happens to that structure. Melting destroys that structure so any area that was melted will undergo changes into a glass at best, and it's unlikely to keep the colour of the original.

Problem number three is: different gems have different crystal lattice that forms different shapes. You can't really make a smooth connection between those.

Problem number four is: different gems are made out of different things, they generally can't be mixed to make a hybrid gem but will make regular "rock" instead.

That means that from the start you would be limited to minerals that are made out of the same things, have similar melting points. Then you can't really cause them to recrystallize appropriately without very specific conditions which are going to be different for two different ones. Gems that can do what you're asking are just a single multicolored gem with different impurities in different locations. Two different ones can't do that because of the reason they are gems in the first place - if you mix them they lose what made them gems.

https://www.geologyin.com/2021/07/watermelon-tourmaline-what-is.html

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QuitBeingALilBitch t1_j69ck9t wrote

I'm aware that melting changes the structure, and I didn't say it would keep the color, I even suggested that it wouldn't have the gradient op was looking for and would be more of a seam than a mixture. I was imagining exactly what you described: two crystals joined by an amorphous obsidian like glass.

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muskytortoise t1_j69f98d wrote

But what's the point then? Gluing them together or placing them next to each other would make for a much nicer final product. Maybe you could use some of the machines used in precision welding but those are designed for metals, so you would most likely need a custom one. In theory you can "melt together" any two objects that can melt but if the final result is completely irrelevant then what's the goal?

Either way, while I wasn't able to find studies that checked thermal stress in any gemstones I strongly suspect the crystals would crack if exposed to temperature gradients required to do that.

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Equoniz t1_j69gmy2 wrote

I’ve seen a (presumably not faked, but 🤷‍♂️) natural gemstone posted somewhere on here that was a different type on either side of the stone. I forget what they actually were (I think they were purple and orange though, so maybe amethyst and…something orange?), but is there a natural process for producing this sort of thing? I’m assuming it would be very dependent on the exact stones, and wouldn’t just work with any combo, if it’s possible at all. Maybe it was the same type of crystal with different impurities?

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CrustalTrudger t1_j69n5ai wrote

> Maybe it was the same type of crystal with different impurities?

Most likely. You can get things like gradations between amethyst (a purple type of quartz) and citrine (an orange type of quartz) in a single crystal because it's all quartz with different things substituting into the lattice. Some minerals can have really complicated intergrowths and gradations of versions themselves, e.g., tourmaline does all sorts of weird stuff, but importantly all have effectively the same lattice structure.

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42nbeyond t1_j6aihka wrote

You can get natural bicolour tourmalines, that would make for a very cool ring. They are usually green and purple, I believe.

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Shambud t1_j6aq1p4 wrote

Tourmaline mine near me pulls up one’s that look like slices of watermelon, red-white-green. They’re cool looking stones for sure.

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copperpoint t1_j6bashd wrote

Ok random slightly relevant bit of info. If you're trying to melt amethyst, as you heat it it will turn into citrine. This happens long before it melts and if you stop the process partway through you get ametrine, which is a solid crystal that is part amethyst and part citrine. You could carve that into a ring and it would look cool but probably be incredibly brittle.

EDIT: I know they want sapphire but they can be yellow so it might have the look they want. And another hindrance to OPs idea is the fact that a gem quality sapphire large enough to be carved into a ring would be fairly expensive.

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eyrieowl t1_j6by87q wrote

So here's a thought: could you take a corundum crystal and dope one portion with Fe Ti to get a sapphire blue, and the other part with vanadium to get an amethyst hue. It wouldn't be exactly the all, but it would give the look of it. I have no doubt it would be prohibitively expensive to figure out the process, but... Is that even theoretically possible?

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