ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Uneven, Conchoidal, Gems, Sixth Edition (2006)
Perfect on {010}, good on {100}
Perfect on {001}, less perfect on {010}, intersecting at near 90°; distinct on {110}