Author's note: Many thanks here to everyone who gave me ideas in the "Gemstone magic" thread. The thread is here and there are many, many good ideas in it:
http://www.rpgcitadel.com/guild/index.php?topic=1240.0
This post is a collation of the ideas I eventually decided to use.Of Gemstones (Extract from a teaching primer at the University of Linnarson, Laurentia, 1770SS) One of the major sources of magical power for the wizards in our world are gemstones. The ability to recognise and identify gems and the methods of extracting mana from them are fundamental skills for all mages, and should be mastered by you early in your training. Only the most flawless gems are suitable for wizardry, meaning the many almost flawless gems (that might, to the untrained eye, appear flawless) are available for their common use as jewellery and ornamentation.
Only the most powerful nobles or royalty would be likely to have gems of magical quality as jewellery, and in such cases the gems would almost certainly be imbued with powerful magical spells. The royal regalia of a kingdom is frequently a collection of items of inestimable value. In fact, any magical item or artifact must contain a gem in order to anchor the spell.
Unfortunately for us, gems are an exceptionally rare commodity in the world. This was not always the case: at the time of the Second Covenantal Charter, gems were far more common: this is largely the reason behind the great mastery of magic in this era. However, gems turn to dust once used, and in our age, a millennium and a half later, the gem mines have been largely worked out. Despite the constant search for improvements in mining technology, the quest for gems becomes harder each year. Some are, of course, still found, but the great lodes of yesteryear are gone for ever. Consumption has fallen of course, as the price and value of gems has climbed, and currently supply approximately equals demand. It is not difficult, however, to foresee a time – perhaps in another millennium’s time, that gems will have become almost non-existent and mages will have to rely purely on their own innate power. Many spells will become impossible to cast. It is for this reason that so much research is devoted to the quest for artificial gems: as yet we have only had the paltry success of mana crystals: colourless faux gems which are very costly to create and produce a pittance of mana; furthermore they are tied to no domain and so cannot be used as spell components. Nevertheless, there was a time, not so long ago, when even this would have been impossible so we retain our hope.
The mining of gems is a difficult and dangerous task. Not only are the current gem mines so deep and inaccessible physically, there is also the fact that large concentrations of gems, especially uncut gems, attract magical creatures which feed upon the energy which they radiate. Elementals, wraiths and spectres are particularly attracted to these energies, and these are all dangerous foes. It is particularly difficult to defend against these magical creatures due to the difficulties of casting magic in mines. Anyone casting a spell near the presence of large quantities of uncut gemstones is playing with fire. Unless controlled extremely precisely, there is a strong likelihood that the magical energies of the spell will course the gemstones to resonate wildly, ultimately creating a devastating massive explosion. The more powerful the spell, the greater the risk of resonance; even the most skilled mages cannot cast with impunity. Ever since the Phloem disaster of 1368SS in which 337 people were killed and a fabulously rich vein of rubies was destroyed, any spell casting in mines has been banned in almost all of the nations of Laurentia.
Naturally, given their power and value, almost all mines are directly controlled by the government of the kingdom in which they are located. The more powerful stones (such as diamonds, rubies, emeralds) are frequently subject to strict government control; it can be very difficult for private individuals to obtain such stones. The difficulty of otherwise obtaining gems is a major factor in prompting many wizards to work directly for their governments. It should be noted that a large black market exists in gems, both in conventional gems and in the illegal bloodstones.
Naturally, of course, almost all governments stockpile gems for use in war. Though gems do not provide ultimate power (a wizard is still limited by the power of his spells), a plentiful supply of gems greatly increases the number of spells which can be used in combat, almost always deciding the day if the gem differential is high enough. In the civilised regions there is not usually a problem of magical creatures being attracted to the stockpiles (due partly to the fact that they are cut, and partly to the fact that we have cleared such hostile creatures from our lands); however, there have been cases of frontier regions suffering raids by elementals upon their gems.
As you may be aware, there has been a small backlash against these phenomena, in the form of the Society for Simple Wizardry. The Society speaks against the use of gems in magic, saying that their use leaves inevitable to corruption, politicking and greed. Not surprisingly, the Society has little power and is mainly the province of young or poor wizards: in fact, the majority of its members are quick to recant once they become successful enough in their field to afford gems of their own. Nevertheless it must be said that the Society of Simple Wizardry has made some successful progress in researching and developing spells without gemstones: whilst as Society wizard is much restricted by his refusal to use gems, if you had no gems available then a Society wizard would likely prove much more useful and versatile than one more conventionally trained.
Regarding the use of gems, it should be remembered that it takes several minutes to attune yourself to a gem before you can use it, though experience can lesson that time. It is thus usually not possible to touch a person’s gem and use it instantly. Many wizards find that setting their most valued gems in to staffs or rings (frequently only of copper or brass) in order that they may be more readily available, and to help protect them against pick-pockets. This, and the fact that a cut gem provides far more mana than an uncut one, means that many mages choose to learn something of the art of gem-cutting and jewellery. Remember: any jeweller you meet may really be a wizard. Due to the power of gems, many places require wizards to turn in their gems at the door (for example, many kings do not allow gems in their presence, in the same way that they do not allow people to carry weapons).
Before we end, two special cases of gems should be mentioned. The first is the mood stone, an exceptionally personalised item of great value. Any wizard of sufficient power can create a mood stone; in fact, some of the most powerful wizards have been known to have as many as three. The process is lengthy and laborious taking several days; it is also extremely draining to the wizard, for it takes an irredeemable toll upon his vitality and life force. In the end though, a mood stone of imperishable and almost unbreakable crystal will have been created, which will give him a reasonable amount of mana. Furthermore, unlike ordinary crystals, the mood stone does not crumble to dust once used; instead, it can be recharged again and again by merely spending the amount of mana to charge it and applying a drop of the owner’s blood.
A mood stone is a personal object: it will change colour and appearance depending on its owner’s mood and personality. If calm and happy the mood stone will appear smooth; if angry then furious currents of energy will appear to move beneath the mood stone’s surface. The colour of the mood stone reflects two things: firstly, the domains chiefly used by the owner (power=gold, fire=red, earth=green, water=blue, air=white, mind=brown, conflict = orange, healing=yellow, death=black). Secondly it will reflect his sense of purpose and honour; the higher and more noble his aims, the brighter and lighter the colours will be. These two factors combine to give a variegated mix of colours through the stone. Finally, the stone will appear dull when uncharged and bright when charged. The highly personal nature of a mood stone means that a mood stones will crumble in to dust if their owner is killed; furthermore, if a mood stone is taken away from it’s owner for more than 24 hours then it will crumble to dust.
Far more sinister than mood stones are bloodstones, used by those who practice dark magic. Bloodstones are formed by the last drops of blood "crystallising" when any draconic creature (including dragons, wyverns, basilisks and firedrakes) is killed in a way that involves bleeding. Especially given the fact that these creatures are usually intelligent, the use of blood magic, which is usually in any case used for dark purposes such as the creation of undead, is banned almost everywhere in the world. This does not, of course, prevent a flourishing black market in bloodstones – many mages are quite willing to compromise their morality in exchange for a more readily available source of power than common gems.