Gems, Sixth Edition (2006), Gems, Sixth Edition (2006), Uneven
ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
Na(90-70%)Ca(10-30%)(Al,Si)AlSi 2O 8Michael OâDonoghue , Gems, Sixth Edition (2006)
Al 2Be 3Si 6O 18Martin H.