Serpentine

Serpentine was the name given to a wide variety of related materials known as williamsite, ricolite, verde antique, picrolite, taxoite, bowenite, or poor man's jade.

Description
These semi-precious stones used extensively for carving are traded as serpentine stone. The finer stones are a vivid pure green while the lesser value stones are a dull green or have white mottling. In the Realms, good stones were widely used in cabochon form, set into ornamented weaponry and harness, rings, and courtly jewelry of all types. A typical specimen had a base value of 50 gp.