ConchoidalWalter Schumann, Gemstones of the world (2001), ConchoidalWalter Schumann, Gemstones of the world (2001)
ConchoidalGemdat.org, Management Team (2012), ConchoidalGemdat.org, Management Team (2012)
SiO 2Ulrich Henn and Claudio C.
(Fe,Mg) 3Al 2(SiO 4) 3gemdat.org , Management Team (2012)