Tenacity
Solubility
Durability
Specific Gravity
Fracture
Cleavage
Mohs Hardness
Chemical Composition
SiO2, Al2O3, FeO, MgO, CaO, K2O, Na2O
slightly water soluble and in hot hydrochloric acid
Subconchoidal, Uneven, ConchoidalWalter Schumann
Octahedral, perfect on {111}, parting on {011}