From "back cover" of PDF:
Within these pages are descriptions of every gem from the DMG, and various ways to identify and use these in your game. They are more than just portable currency. You‚ll learn how to identify cut stones and find new rules pertaining to the appraising and crafting of finished gems. You will also find that some stones have purposes other than trade or adornment, both mundane and magical. You‚ll see that some stones and crystals can be used in curative poultices, salves, and remedies, as well as mundane charms. Many stones contain long-sleeping magical energies, just waiting for someone to learn the ancient methods to unlock the latent wonders hidden beneath their many facets.