Webstone

Webstone was the Realms name for spiderweb obsidian.

Description
This ornamental stone was an obsidian variety in which small pieces of the stone were cemented together by heat and pressured in an irregular mass, the joints showing as irregular, web-like lines. It was usually black, the join lines sometimes showing white, but brown, reddish brown, and rust-red varieties were found. A typical stone had a base value of 10 gp.