Sheen

Sheen was a variety of obsidian with many tiny sparkles. If the spangles were gold in color it was known as gold sheen and was classified as a semi-precious stone with a higher base value.

Description
Sheen came in many colors ranging from mahogany to russet to silver to gold. If large and without flaws it was usually tumbled and polished. Otherwise the flaws were cut away to make cabochons. Sheen could be polished to a satiny gleaming finish. A typical stone had a base value of 10 gp.

Powers
Sheen could be added to the material component of any spell that created light or radiance and allowed the caster to control the color of the emissions very precisely. If added to invisibility spells, it increased their duration by up to three minutes.