Jasper

Jasper was a form of opaque chalcedony found in reds, browns, and blacks.

Description
Very rare specimens of these semi-precious stones were blue or had bands of blue against the other colors. Jasper was crushed and used in making potions and magical devices which protected against poison. Jasper was used in periapts of foul rotting and proof against poison. A typical specimen had a base value of 50 gp.