Gems, Sixth Edition (2006), Gems, Sixth Edition (2006), Uneven
Conchoidal, Brittle, Conchoidal, Brittle, Conchoidal, ConchoidalArthur Thomas, Gemstones (2009), Brittle, Conchoidal
Na(90-70%)Ca(10-30%)(Al,Si)AlSi 2O 8Michael OâDonoghue , Gems, Sixth Edition (2006)
Fe 3Al 2(SiO 4) 3Arthur Thomas , Gemstones (2009)