Uneven, Conchoidal, Conchoidal to uneven, Brittle
Subconchoidal, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Conchoidal
On {10 1 1} perfect; parting on {10 1 2}
Perfect on {001}, poor on {201} with 38.5° angle between the two