Conchoidal, Conchoidal, Gemstones of the world (2001)
Sub-Conchoidal, ConchoidalArthur Thomas, Conchoidal, Uneven
SiO 2 · nH 2OWalter Schumann , Gemstones of the world (2001) More from other references
(Fe,Mn)AlPO 4(OH) 2 -H 2OArthur Thomas , Gemstones (2009)