Vargo Hoat, Game of Thrones G.R.R. Martin.
A sapphire is, essentially, any first order corundum gemstone that isn't a ruby - that is, one that is any colour but red. The archetypal sapphire is blue, but they can be of virtually any other colour including off-red/pink and green (sometimes misclassified as emeralds).
Like all other precious stones, their value is governed by the "four Cs" (colour, clarity, cut and carat weight), but carat for carat they are less valuable than rubies and more so than emeralds, making them number three amongst the first order gems. Colour will affect value dependant on cultural issues - sometimes the rarer colours have been more sought after, in others it has been the pure blue that mattered and the others have not even been recognised as sapphires. Like rubies, sapphires are prone to asterism, which can substantially increase their value.
Mystically, sapphires have been associated with wisdom, royalty and prophecy, and in Christian tradition in particular with the heavenly firmament and the throne of God. Non-blue sapphires are often assigned additional significances. It is the stone of Saturn, particularly associated with the zodiac house of Virgo and is the birth stone of the month of September.
In modern usage, being hard, but more workable than diamond, sapphire is favoured for high precision parts such as watch bearings and scientific instrument parts and is also a popular insulator for use in semiconductor assemblies.
Game and Story Use
- Green or pink sapphires may confuse the less well informed player. Characters, on the other hand, should know whatever it would be reasonable for them to know … especially if they have relevant skills. Note that it might well be reasonable for an in-game culture to call all first order green gems "emeralds" and so present the chemical impossibility of a "star emerald" (a green sapphire with an asterism).
- Equally, it's fine to simplify things in game - non-blue corundums might actually be sapphires, but if in-game cultures don't consider them such, then they might as well not be. Corundum stones that are neither blue nor red might have their own class…