Wonderstone

Wonderstone was a variety of rhyolite displaying bands of red, brown, tan, or purple.

Description
These ornamental stones were found in large deposits, and could be cut into blocks of almost a cubic foot (27,000 cubic centimeters) in size when quarried. It was typically cut cabochon, and took a fair to good polish. A typical stone had a base value of 10 gp.

Powers
When wonderstone came into direct contact with a magical item, an enchanted being, or an ordinary item that bore an enchantment, it emitted a royal blue or strange blue-green glow for up to twenty minutes. Thus it saw some use as a magic detector, but more often was put to mundane use as an inlay in fine furniture and paneling to provide novel mood lighting for light-hearted social events like balls, feasts, and parties.