This sliver of a gem is very light, almost without substance. It seems to be made from crystallised ectoplasm.In-game description
Wispstone is an item in the MARDEK series. It can be equipped in either Accessory slot by Mardek, Deugan, Emela, Steele, Vehrn, Zach, Donovan, Sharla, Sslen'ck, Solaar, Elwyen, Gloria, Meraeador, Legion, Bartholio and Aalia.
Wispstones are small, turquoise gemstones. They appear to actually be made out of a crystallized liquid in an odd position, like if one were to petrify a piece of honey that was about to fall. Wispstones are presumably either made of hollow turquoise, crystallized ectoplasm (as the description suggests) or out of the corpse of some ethereal creature. They have a unique sprite.