Urdunnirin looked much like gold dwarves. Their skin and hair, however, were stone gray and their eyes were silver. Males groomed their gray beards carefully, while females did not have facial hair.
All urdunnirin had the ability to walk through solid earth and stone at will, moving through these normally solid materials as if they were air. They could move up to twice their body weight with them in this manner. They also had an innate ability to shape stone and metal as if they were wet clay, the materials remaining solid after they were done with them.
Urdunnirin did not eat normal foods. Instead, they fed on gems as xorn did. The god Dumathoin provided each urdunnir settlement with a self-replenishing gem supply so that his people did not starve. They guarded these sources to the death.
Urdunnirin were deadly enemies of the xorn, and killed them on sight.
Urdunnirin were led by alirds, or gold lords, whose power to shape metal was greater than usual for the race. Urdunnirin had a clan-based society, like most other dwarves. Known clans included Marble, Gold, and Ruby.
Urdunnirin wore tight-fitting, one-piece garments composed of metal, stone, or both. They used their innate abilities to make these garments flexible. Only their leaders wore clothing completely composed of metal. 
Dwarven myth said that urdunnir were specially blessed by the god Dumathoin.