ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
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Al 2Be 3Si 6O 18Martin H.
(Mg,Fe)Al 2(PO 4) 2(OH) 2Arthur Thomas , Gemstones (2009) More from other references