There are eight creature Composition Types in Dwarf Hammer, each which, like the twelve Chinese Zodiac, modifies a creature's base stats and/or gives them some sort of special ability or resistance. The composition types are Flesh, Stone, Limestone, Diamond, Charcoal, Glass, Crystal, and Gas.
A creature's composition type can be altered using the high-level spell Transmog. This is one of the basic survival strategies of the later portions of the game. Your flesh dwarf cannot be directly transmogged but can bounce a Transmog spell off a glass creature.