"Hee! hee! hee!" cackled old Gagool behind us, as she flitted about like a vampire bat. "There are the bright stones ye love, white men, as many as ye will; take them, run them through your fingers, eat of them, hee! hee! drink of them, ha! ha!"
King Solomon's Mines H. Rider Haggard.
A gemstone is piece of stone or mineral crystal that has significant economic value due to its appearance and/or rarity. Traditionally gems are cut into shapes which enhance their appearance and/or polished before setting into ornaments or jewelry but even unset they have often been used as a portable store of value. Hence, they also play an important part as valuable treasure - usually far more portable then specie currency.
The actual market value of a stone will depend on the supply, the degree to which that stone is valued culturally by the buyer and on the features of the stone itself - the traditional "four Cs1" and other factors such as visible patterns in the matrix of the stone. Historically some stones were also said to have magical/medicinal properties which would further enhance their value. An uncut stone is usually worth far less than its potential "finished" value and may be extremely hard for a layman to identify, especially if it is also unpolished. That said, historically the "big four" (ruby, diamond, emerald and (blue) sapphire) have traditionally composed the "first order" of gemstones, sometimes accompanied by pearls, and the primacy of diamonds is extremely recent, the laurels generally going to the ruby in previous eras.
It is also worth noting that gem-cutting technologies can vary enormously - for much of the historical middle ages, it was more common to cabochon and polish a gem than attempt the risky business of cutting it into facets … especially in the case of diamond, which was so hard as to be regarded as almost unworkable for a long time. As a result a variety of "rock crystals" which would be considered only fit for costume jewelry in the modern era were actually a viable proposition. Also, before modern analytical techniques, confusion could exist as to the identity of some stones - green sapphires have sometimes been misclassified as emeralds and various garnets and spinels mistaken for rubies.
The category of gemstones can also include organic compounds such as diamond and amber and biologicals such as pearl, all of which fit admirably by function and until the invention of modern glassmaking techniques, glass was seen as an equivalent, rather than an imitation material for setting into jewelry. Sumptuary laws traditionally have quite a lot to say about who can wear what stones dependant on their social status, as, in differently organised societies, can taboos.
Traditionally - and probably at least partly due to their value - gemstones have also been assigned mystical qualities. These can be determined based on any mythical connection to some deity, from correspondences to various astrological phenomena or from observations based on the colour of the gem.
A page considering the supposed magical uses of gemstones
Another guide to gemstones -with useful accompanying pictures and access to magical properties.
Game and Story Use
- The alleged magical properties of stones should be interesting for someone writing a magic system - they may be useful as focii for spell casting or even power-enhancing consumables.
- As small, valuable, portable objects they make a good way of transferring large quantities of money covertly - for PCs involved in criminal or espionage campaigns, they may be an important tool.
- They can sometimes prove to be a better store of value than a source of value - for PCs without the right connections, getting the 'correct' price for their gems when and where they need it may be an adventure in itself.
- Combining the last two, someone suddenly selling a lot of unmounted gems may be a clue that something interesting has just started.
- Some traditions hold that large gemstones provide homes for malevolent spirits - and generally the bigger the stone, the worse the inhabitant, as in the traditions of the Hope Diamond or Wilkie Collins's The Moonstone.
- This may be used in a magic system to have gemstones used as vessels in which spiritual entities can be bound - the bigger the stone, the more powerful the entity. Possibly an exception to the idea that a fetish is typically made of biological materials or possibly a different approach (perhaps a shaman uses organic fetishes, whereas a sorcerer traps and binds spirits in stone. Naturally occurring spirit traps, complete with trapped (and therefore angry) but unbound spirits may be behind the rumours of cursed stones.
- For those that like their elemental correspondences the diamond/air, emerald/earth, sapphire/water and ruby/fire correlation seems appropriate.