Heroes of Greyhawk
Gem of Seeing
This finely cut and polished stone is indistinguishable from an ordinary jewel in appearance.
This oval-cut diamond has two flat, highly polished surfaces. The stone is about 1-inch in diameter and a quarter-inch thick. When looking through the gem as a lens, the user sees all things as they actually are. The Gem of Seeing can pierce normal and magical darkness, notices secret doors hidden by magic, sees the exact locations of creatures or objects under blur or displacement effects, sees invisible creatures or objects normally, sees through illusions, and sees the true form of Polymorphed, changed, or transmuted things.
A character can focus its vision, using the Gem of Seeing, to look into the Ethereal Plane (but not into extradimensional spaces). The range of vision through the Gem of Seeing is 120 feet. The Gem of Seeing does not penetrate solid objects. It in no way confers X-Ray Vision or its equivalent. It does not negate concealment, including that caused by fog and the like. The Gem of Seeing does not help the viewer see through mundane disguises, spot creatures who are simply hiding, or notice secret doors hidden by mundane means. In addition, the Gem of Seeing cannot be further enhanced with known magic, so one cannot use the gem to look through a crystal ball or in conjunction with a Clairaudience/Clairvoyance spell.
A Gem of Seeing can be used for as much as 30 minutes a day, divided up into periods of minutes or rounds as the user sees fit.