Sharpstone

Sharpstone, also known as novaculite, was a quartz variety that occurred in various colors.

Description
In the Realms this ornamental stone was commonly quarried as a gritty sharpening stone, it was sometimes fine enough for gemstone use, cut cabochon. It was difficult to polish to a high luster, but could yield large stones. A typical stone had a base value of 10 gp.