Nelvine

Nelvine was the Realms name for a variety of feldspar called albite which was found in large quantities in older rock formations.

Description
The gem quality version of these ornamental stones had a blue iridescent flash known as peristerism. Nelvine was soft enough to be easily cut with even crude tools, but it was too fragile for fine detail work. The base stone was usually white, cream, fawn, or brownish pink and was therefore sometimes called a "pigeon stone". A typical stone had a base value of 10 gp.