Woodtine

Woodtine was a variety of cassiterite.

Description
This brownish and fibrous ornamental stone was found in large nodules and was cut cabochon. The name of this stone was a corruption of the odd term "wood tin", applied colloquially to this gemstone. A typical stone had a base value of 10 gp.

Powers
This gemstone could be used as "residual magic" detector, more sensitive than detect magic and other similar spells. When woodtine was brought into contact with another gem, stone, or metal, it would darken in color if that item had been previously enchanted and had since released its magical energies. The color change was temporary and repeatable.