Arcanite (3.5e Equipment)
From D&D Wiki
Wondrous Item, very rare
Arcanite is a crystal usually no more then 3" long is found almost never in nature with the only exceptions being an area with a unusually high level of ambient magic to the point where it begins changing the environment in some way.
Arcanite is coveted by all arcane magic users for its ability to seemingly bypass many know limits to magic, however the crystal is always unstable and even a 6" drop will undoubtedly cause it so shatter and explode dealing 6d6 damage(no type) in a 10ft burst. Knowing this many mages still seek it out as if properly contained and protected it can be use to replicate most spells even a limited wish if done properly though most never succeed and the lab is a ruin to be discovered many years later.
Should a player actually find this rare, and almost unheard of crystal the possibilities are vast. a golem animated for no spell/xp cost though the body must still be made, enchantments that are far more powerful then originally intended i.e. a flaming sword that does +10 fire damage instead of +2(note most enchantments must be done in a safe room devoid of other magic sources to avoid incidental amplification of unintended sources)
a typical crystal usually sells for over 20,000 gold pieces on the black market as no sane merchant would handle such a find