The color of cordierite comes from its Fe2+ and
Fe2+ in the octahedral site causes the pair of
near 1000 and 1300 nm which have almost no effect on the color. The
absorption band in the gamma direction is also from Fe2+,
in a different site. The color is predominantly due to the Fe2+
- Fe3+ intervalance charge transfer band near
600 nm. Sharp
bands near 1400 and 1900 nm are from water molecules in channels which
run parallel to the c-axis of the crystal.
Visible Spectra: polarizations: (a = alpha direction; b =
g = gamma direction)
262 spectrum; Cordierite, GECO Mine, Manatowage, Ontario,
Canada, 0.5 mm thick With type I water dominant.
Data Files: a; b; g