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I'm currently working on a conworld that has never had any contact with Earth, and I'd like to create words for iconic gemstones, such as rubies, emeralds and sapphires.

However, I can't help but wonder: Are these gemstones "universal", or are they unique to Earth?

Is the existence of these minerals linked to unique events in Earth's history, like the evolutionary histories of organisms?

Or is the process behind their formation simple enough that they could emerge just about anywhere where the right elements are present?

I realize that a general answer might not be possible, but even a push in the right direction would be helpful to me.

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    $\begingroup$ Chemistry is chemistry, and physics is physics, so yes. $\endgroup$ – RonJohn Apr 2 '18 at 13:28
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    $\begingroup$ Yes and no. Rubies and sapphires are both aluminum oxide with impurities. Rubies have a red color, any other color is a sapphire. It seems unlikely that on a different planet that the same sort of distinction would be made. $\endgroup$ – MaxW Apr 2 '18 at 20:56
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    $\begingroup$ @MaxW Indeed, how they would actually be categorized is yet another thing to consider when designing a language; they might use the same word for rubies and sapphires, or make even greater distinctions. However, as a first step, it's interesting to consider if they would exist at all. $\endgroup$ – loghaD Apr 2 '18 at 21:15
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    $\begingroup$ @MaxW I'd reason that any society that finds naturally occurring rubies and sapphires before having the technology to realize they're both aluminum oxide would have different names for them. Assuming those are the most common colors; dunno if you normally find the whole spectrum of colors in the same place. $\endgroup$ – JollyJoker Apr 3 '18 at 11:05
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    $\begingroup$ Yes $\endgroup$ – Obie 2.0 Apr 4 '18 at 3:47
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Crystal structure is dictated by Gibbs free energy. Once you have the right chemicals and the right conditions, nothing prevents the formation of the desired gems.

The only gems you would not generally find are those with organic origins, like

  • amber (resulting from fossilized tree resin)
  • jet (resulting from decaying wood under high pressure)
  • abalone (resulting from shell fish)
  • ammolite (resulting from fossilized ammonites)
  • ivory
  • [...] other
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    $\begingroup$ Interestingly, should those planets have life, we might find organic gems that do not exist here :) $\endgroup$ – Renan Apr 2 '18 at 14:09
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    $\begingroup$ if you are counting ivory, you might add pearl as well. $\endgroup$ – Skyler Apr 2 '18 at 18:52
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    $\begingroup$ @Skyler, right. There are also other I didn't include in the list $\endgroup$ – L.Dutch - Reinstate Monica Apr 2 '18 at 19:23
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    $\begingroup$ add to that marble (metamophosed limestone, the bulk of which comes from reefs) and coral (obvious) $\endgroup$ – 16807 Apr 2 '18 at 20:28
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    $\begingroup$ I don't think there's much meaning in listing all possible rock-like things with organic origins, this isn't mineralogy stackexchange after all $\endgroup$ – Cubic Apr 3 '18 at 9:01
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MOST of the gems would either be the same or have close analogs. Depending on chemical abundance, you may have different combinations. Gem colours are usually impurities -- ruby is chromium.

You may get gem quality stones of things that normally don't form gems here. E.g. natural cubic zirconia has been found, but only microscopically. There are some oddball gems that are uncommon on earth that may be common there.

I would certain expect all the stones based on quartz and corundum (silicon dioxide, and aluminum oxide) Amethyst and kin, sapphire and kin to be present.

Suggest reading up on Wiki on the particular gems you have in mind.

https://en.wikipedia.org/wiki/List_of_minerals

gives you a good start. Many are not observed to be gems, but it gives you a lot to play with.

If you want different ones, you have to do some worldbuilding geology -- see if you can come up with a plausible way to come up with different crystal structures. This may be accomplished by having radically different concentrations of metals, or perhaps something different in the way of solvents. (Could you get different crystals on a world that ran 10% ammonia for it's liquid phase...)

Some stones can be modified by heat. Heating them will change the colour. The colour of amethysts is influenced by radiation

Another way for different gems are biological origins. In Piper's Fuzzy series, the planet Zarathustra has "sun stones". Apparently if a certain jellyfish died, and was embedded the right way, it turned into a stone that was thermo-luminescent.

Petrified wood is another example: different parts were replaced at different times, and hence have differing colours.

Look at microscopic pictures of radiolarians. Imagine such a critter much larger. Imagine them with crystaline sapphire skeletons.

If you want to have fun, put down gems that cannot be grown by natural processes, but instead have to be built by a molecular assembler. (What kind of gems could you get with a fractal array of copper inside? Or gems that have books coded into them. Gems that are in effect 3d hologram encoded picture catalogs.) You can justify this with a culture that is trying to leave a really long time record. 5 carat holographic diamonds, made by the trillions. With layers of information in them that required more and more sophisticated tools.

If you are going to make artificial gems, look at making them with unusual symmetries. square, triangular and hexagonal symmetry is common. Mirror, pentagonal is more rare. Heptagonal (7 way) is unknown.

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The short answer is yes - they would be universal depending on the original composition of the planet.

Gemstones are actually crystalline forms of Aluminium Oxide, with impurities inside to give them colour, such as other elements like Chromium (to form Rubies) or other metals to form emeralds and sapphires.

These Aluminium Oxide crystals are usually formed in standard tectonic or high pressure magma compressions deep within the planet, standard forces over time bring them closer to the surface. This would be common on most rocky core iron-rich planets similar to Earth.

Aluminium itself is one of the elements on Earth that has existed since its formation and likely came from the preexisting dust that made the solar system. It is formed usually in large stars or supernovae - by fusing hydrogen and magnesium.

It is reasonable to assume other systems of similar generational age follow a similar route of formation, and thus aluminium would be present in other systems. Because of aluminiums strong tendency to oxidise, and the ever-present nature of oxygen, it is reasonable to assume there is a likelihood Aluminium Oxide which may give rise to gemstones elsewhere.

However, we are still learning about exo-planetary formation, in fact it wasn't too long ago that we hadn't detected any at all - however we can be fairly certain that given similar age and conditions, it would be possible to recreate the processes that naturally gave rise to gemstones.

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    $\begingroup$ Rubies and sapphires are indeed beautiful forms of corundum (crystalline aluminium oxide). But emeralds are a different mineral -- they are beautiful forms of beryl (beryllium aluminium silicate). $\endgroup$ – AlexP Apr 2 '18 at 14:44
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    $\begingroup$ @AlexP Oops - yes - I was only assuming the OP was referring to Rubies and Sapphires and neglected to look to emeralds. Apologies you are correct. $\endgroup$ – flox Apr 2 '18 at 15:12
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    $\begingroup$ gemstones can be made of lots of other things as well, plenty of gems are not aluminum based; jade, lapis, citrine, diamond, jasper, onyx, ect $\endgroup$ – John Apr 2 '18 at 21:34
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    $\begingroup$ expanding on @John most gems on the planet are actually quartz varieties and are therefore sillicon dioxides $\endgroup$ – tox123 Apr 3 '18 at 1:53
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The elemental composition of planets varies widely and even two earth like planets might have a big difference in which elements are most common vs uncommon. That would effect which gems, minerals and metals would be the most rare on each planet. There would also be variations in geology that would effect which formations were most likely. Certain minerals and gems have different crystal structures in different parts of the world. Take a look at some differences found within different regions of earth to get some ideas of what could be possible on other planets.

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    $\begingroup$ I think the point about rarities may be worth emphasizing even more. Many "gemstones" on earth are simply uncommon varieties of common minerals. If the distribution of minerals is very different on another planet, entirely different minerals might be considered to be gems. So maybe quartz is incredibly rare and precious, but diamond is an ubiquitous material that nobody thinks is valuable (e.g. you make windows out of giant diamonds cut into sheets). $\endgroup$ – Blckknght Apr 3 '18 at 0:59
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    $\begingroup$ @Blckknght : How do you cut a diamond into sheets? $\endgroup$ – Martin Bonner supports Monica Apr 4 '18 at 11:47
  • $\begingroup$ @MartinBonner - with other diamonds? $\endgroup$ – Megha Apr 5 '18 at 2:33
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There are two questions you ask. L.Dutch provided very nice answer on possibilities of existence such structures elsewhere.

The other question is whether they are about to be identified as valuable gemstones.

Gemstones are usually scarce and used in jewellry. Synthetic gems (diamond for cutting tools, ruby for lasers) are significantly cheaper while they have very same structure and sometimes fewer impurities.

Another example is gold. In Middle-ages Europe it was scarce and highly valued metal, in a New World it was used as a sacrifice to the gods. In Terry Pratchett's Discworld, gold is scarce and highly valued metal everywhere except for a Counterweight continent, where it is just a common, soft, yellow metal.

If you are asking whether an earthling can find gemstones somewhere on a distant Earth-like planet then yes, it is highly probable.

If you are asking whether inhabitants of a distant Earth-like planets would treat such special structures differently, then it depends on the cultural backgroud you make for them.

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Depends on what you mean by "earthlike". If you mean as the conditions to sustain life -- i.e. a rocky planet orbiting a star's habitable zone, with a moon and not tidal locked to the star (thus, having day-night cycle, liquid water, rains, analogous climate, magnetosphere, etc), that is not enough to say the same distribution of chemical elements on the solid surface, the rarity and availability of some gems may vary greatly.

But if by "earthlike" you mean not necessarily habitability, but composition, mass and tectonic activity (which would also require a moon with similar orbit and mass to the Earth's moon), then I believe the mineral distribution and rarity would be very similar to Earth's.

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