ConchoidalArthur Thomas, Gemstones (2009)
Conchoidal, ConchoidalArthur Thomas, Gemstones (2009)
(Mg,Zn)Al 2O 4Gemdat.org , Management Team (2012)
(Ca,Fe,Mn,Mg) 3Al 2BSi 4O 15(OH)Walter Schumann , Gemstones of the world (2001) More from other references