TL;DR: Without lasers, electricity, or otherwise modern tools, could large transparent gems be sliced (like glass window)?

So I’m world building. On this planet they have caves with enormous gemstone/crystal/pretty mineral structures (think lechuguilla) which they mine and most often tumble for currency. It occurred to me that they would use these for windows if they could manage to somehow slice the stuff. It could be useful to know, their water-based tech is pretty advanced and certain regions have created small magnet-powered motors.

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    $\begingroup$ I'm voting to close this question as off-topic because it belongs to World Building SE $\endgroup$ – Camilo Rada Mar 15 '19 at 4:54
  • $\begingroup$ No it does not. I need the information for world building. The question has nothing to do with that. The question is: can humans slice gemstones? I promise you, the world builders do not accept these questions. $\endgroup$ – Bett Struble Mar 15 '19 at 4:58
  • $\begingroup$ I'm afraid this question is probably off-topic here. However, you might want to consider that some crystals can naturally grow with a plate shape. Ice crystals for example, can take an hexagonal plate shape, and other minerals crystallize in the same fashion. Therefore, under the right conditions, crystalline plates could grow to a size large enough to make them practical to be used as windows. $\endgroup$ – Camilo Rada Mar 15 '19 at 5:00
  • $\begingroup$ If you want to get an answer here I would suggest to remove the world building part of the question and be more specific about the gemstones you are considering. If your range of gemstones include gypsum crystals, the answer most probably will be yes, if it only includes stuff like diamonds it might be no. Also, the way gemstones were worked in the past was not by cutting but by polishing, and with stone age technology you can certainly polish almost any crystal into a flat sheet as a normal window glass. $\endgroup$ – Camilo Rada Mar 15 '19 at 5:08
  • $\begingroup$ I'm also voting to close this as belonging on WorldBuilding because of the introduction saying we can't use current technology. Even without that and without all the references to WB it would be a borderline on topic question - it's more an engineering one. $\endgroup$ – Jan Doggen Mar 15 '19 at 9:21

sliced (like glass window)

Window glass is not sliced into sheets. It is made as sheets from the beginning.

Since you're looking for a naturally occurring mineral that can be made into a glass-like material, look no further than muscovite.

enter image description here

Because your planet has nice and big crystals, it most likely come from pegmatites, which is a type of rock that has large crystals and many gemstones we know today come from pegmatites (emerald, tourmaline, topaz, kunzite, etc). Pegmatites also have huge crystals of muscovite as well, in some rare occasions several metres wide. Muscovite can be easily split into sheets that are flexible and mostly transparent. Not the best glass material (because it is not glass after all), but almost as good. Quoting from the Wikipedia page:

The name muscovite comes from Muscovy-glass, a name given to the mineral in Elizabethan England due to its use in medieval Russia as a cheaper alternative to glass in windows. This usage became widely known in England during the sixteenth century with its first mention appearing in letters by George Turberville, the secretary of England's ambassador to the Russian tsar Ivan the Terrible, in 1568.

Here's a good video showing how this is working.

So the inhabitants of your planet can mine the other crystals in the pegmatite for currency or whatever, and use the muscovite as building material.

  • $\begingroup$ Another mineral that was used for windows is mica, or isinglass. It was used in old stoves because of its resistance to temperature changes that might shatter or melt ordinary glass: antiquestoves.com/isinglass $\endgroup$ – jamesqf Mar 15 '19 at 18:42
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    $\begingroup$ Muscovite is a type of mica. $\endgroup$ – Gimelist Mar 15 '19 at 20:39
  • $\begingroup$ Thank you! Jesus, people are way too concerned with policing my questions on this site when the people who can answer my questions always wind up using all my information. You're a peach. $\endgroup$ – Bett Struble Mar 16 '19 at 3:55

Gemstones can be cut like any other stone. (Of course very hard ones like diamond & sapphire will be difficult to cut.) One technique used by the Romans and others for stones like marble was to use a bronze blade with a flow of abrasive - quartz sand, probably - in water. Not all that different from a modern diamond blade used to cut stone or tile - the major difference is the electric motor. You could power it with a water wheel instead.

Amethyst is one example of a semi-precious gemstone that forms fairly large crystals (and things like geodes). It's a form of SiO2, so fairly hard, yet slabs of it (and many other semi-precious gemstones) can be readily found for sale on Amazon, eBay &c.

  • $\begingroup$ indeed, quartz is very tough and they cut it into wafers for cpus. rubies are the same. $\endgroup$ – com.prehensible Mar 15 '19 at 7:17
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    $\begingroup$ @com.prehensible: Are you perhaps confusing quartz - silicon dioxide - with the elemental silicon wafers used for integrated circuits? Though quartz is used in electronics, as the most common material for crystal oscillators... $\endgroup$ – jamesqf Mar 16 '19 at 5:06

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