Terralith D10: - Rules of Play says:
Terralith are metal RPG dice that have been specifically designed to be totally different from anything else available today. Traditional dice design is based on the Platonic solid (e.g. a D6 is a cube, a D20 is a Icosahedron etc.) which leaves the dice feeling a bit...mechanical, so the design challenge for Terralith was to create something that breaks away from that without compromising randomness.