AM_Picropharmacolite
Formula: As4 Ca4 Mg O27 H24
Name: Picropharmacolite
Unit cell: 13.547 13.5 6.71 99.85 96.41 91.6 , V=1200.12
Space group: P-1 (2)

Catti M , Ferraris G , Ivaldi G , American Mineralogist , 66 (1981) p.385-391, The crystal structure of picropharmacolite, Ca4Mg(HAsO4)2(AsO4)2*11H2O