Optical Spectra of Stewartite,
MnFe
2
(PO
4
)
2
(OH)
2
´
8H
2
O
Rossman GR (1976) Spectroscopic and magnetic studies of ferric iron hydroxy sulfates: The series Fe(OH)SO
4
·nH
2
O and jarosite. American Mineralogist 61, 398-404.