Gemstones of the world (2001)
ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Brittle, Metallic
Microcline: KAlSi3O8 Oligoclase: (Na,Ca)Al1-2Si3-2O8
Be 2BO 3(OH)Ulrich Henn and Claudio C.