From the publisher's website:
Gemstones and other crystals have long been associated with magic and purity. You only have to think of how crystal balls are used in fiction—often portrayed as the very source of a witch or wizard's powers—to be sure of that connection. Even in modern times, the link has remained strong. Go to any bookstore or new age gift store to see that people today still associate crystals with healing and arcane power. Yet, while you will find crystal balls and enchanted gems in the Pathfinder Roleplaying Game, as a rule they are repositories for generic arcane or divine abilities, not sources of power or iconic items unto themselves.
The Genius Guide to Crystal Magic takes crystals and gemstones beyond the merely cosmetic roles they've had thus far in spellcasting and gives them a magical niche of their own. It begins by discussing the use of crystal foci in a campaign and describing the difference between normal crystals and those particularly suited for use in viewing or healing. Next you’ll find a collection of new spells for all the spellcasting base classes and the addition of a new [crystal] descriptor for spells that tie directly to the heart of crystal magic—healing, scrying, and drawing on the inherent magical power of crystals and gemstones. In addition there are new crystal-themed class options to enable the creation spellcasters whose focus is the magic of crystals. Finally, you’ll see the carbuncle—a new simple monster template to help GMs make crystals a more integrated part of the campaign.