Tenacity
Solubility
Durability
Specific Gravity
Fracture
Cleavage
Mohs Hardness
Chemical Composition
(Ca,Fe,Mn,Mg) 3Al 2BSi 4O 15(OH)Walter Schumann , Gemstones of the world (2001) More from other references
Uneven, Conchoidal, ConchoidalWalter Schumann
Indistinct on {001}; partings on {011} and {111}
FeS 2Michael OâDonoghue , Gems, Sixth Edition (2006) More from other references