Jewel Magecraft

The magecraft that Rin specializes in.
Jewels easily accumulate the thoughts of their owners, and make excellent vessels for magical energy.
Crystals that have slumbered beneath the earth for eons, in particular, are prone to having nature spirits form within them, and jewels with that property can be used as simple magic crests. For example, a jewel with a nature spirit of fire dwelling within it would become highly flammable just by passing magical energy through it… or something along those lines.
Whenever Rin has spare time she transfers her magical energy into jewels, turning them into powerful bullets. However, in the end they are merely disposable items.
Because their magecraft reduces expensive jewels to ash after a single use, the Tohsaka magi are fated to be chronically afflicted with a lack of funds.

Fate/side material: Fate Encyclopedia

The Tohsaka family specializes in magecraft known as Jewel Magecraft, which relies on accumulating magical energy within jewels. Precious jewels end up being used in a disposable fashion, causing significant and persistent depletion of the Tohsaka family coffers.

Translator’s Notes
  1. ^ Also referred to as Jewel Magic.
Fate/Zero Animation Guide I: Glossary of the holy grail war I