Optical Spectra of Tuhualite,
(Na,K)
2
Fe
2
2+
Fe
2
3+
Si
12
O
30
Taran, M, Rossman GR (2001) Optical spectroscopic study of tuhualite and a re-examination of the beryl, cordierite, and osumilite spectra. American Mineralogist 86, 973-980.