Crystal weaving is a lost art that was practiced 1800 years ago in the kingdoms of Devania and Senay; a debased form of the technique still exists among the illiterate homesteaders and hill men of the region. Every so often, a peculiarly driven adventurer explores the ancient lands to uncover its secrets, and some return with mystical powers.

In D&D terms crystal weaving is a special skill possessed by a "prestige class" that makes objects unbreakable or impenetrable.

While I'm still working on the conversion, it seems like this should be a Fine Crafts Secret (possibly more than one) to augment weapons, armor, and other gear. A full-fledged crystal warrior has a skin hard as a rock, can fire crystal shards from his fingertips, and mentally control crystalline growths from the ground.