I am looking for a kind of crystal that can be artificially made at relatively low temperatures (below 1500 degree Celsius) and relatively quickly (not geological time). The product is ideally monocrystalline, not reactive to oxygen or moisture and not metallic. Ice is excepted.
If such a material exist, I would like to know its name, composition and any other noteworthy properties. If there is anything wrong with the premises of the question, please point it out.