Chrysoberyl

Chrysoberyl, also known as a cat's eye, was a hard, transparent, green gem, usually facet-cut.

Description
This fancy stones were used in producing devices which provide protection against magic jar spells or other forms of possession, and in weapons designed to affect ghost and similar creatures. A typical specimen had a base value of 100 gp.

Uses
A chrysoberyl gem could be used for short-range but very detailed scrying. For that reason, it was known as a cat's eye.

Novels

 * Resurrection

Sourcebooks

 * Forgotten Realms Adventures
 * Volo's Guide to All Things Magical
 * Forgotten Realms Campaign Setting 3rd edition