Gold sheen

Gold sheen was a rare variety of obsidian that was considered a semi-precious stone.

Description
This stone had tiny golden speckles in a glassy black substrate, giving it a unique appearance. Specimens were usually tumbled to form cabochons rather than cut because the stones were brittle and did not hold an edge well. When polished, the surface was like smooth glass that let the golden spangles shine through. A typical stone had a base value of 50 gp.

Despite being brittle, gold sheen was once used to adorn shields and belts. Some mercenary companies had a tradition of using unpolished or broken pieces of gold sheen as currency within an encampment.

Powers
This gemstone could be added to the material component of any spell that produced light. It allowed the caster to choose the hue of the radiance precisely. When used as a component in spells that created invisibility effects, a gold sheen increased the duration by up to three minutes.