ConchoidalWalter Schumann, ConchoidalWalter Schumann, Gemstones of the world (2001) More from other references, Splintery
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Na 4Al 3Si 9O 24Cl to Ca 4Al 6Si 6O 24(CO 3,SO 4)Walter Schumann , Gemstones of the world (2001) More from other references
(Mg,Fe2+ ) 5Al(Si 3Al)O 10(OH) 8Anthony et al , Handbook of mineralogy (2001)