Micas usually owe their color to Fe, Mn, Ti, and Cr. Iron contributes as Fe2+,
Fe3+, Fe2+ - Fe3+ intervalence charge transfer, and as
Fe2+ - Ti4+ intervalence charge transfer. Manganese contributes
weakly through Mn2+, and strongly through Mn3+ and associated color
centers induced through natural radiation damage. Chromium in the 3+ oxidation state
contributes an intense green color to some micas.
Manganese-containing micas
- pink lepidolite image, 7K;
Lepidolite, GRR 678, Himalaya Mine, San Diego County, California, 1.0 mm thick
with Mn3+ in octahedral sites dominating the spectrum.
Data Files:
a 13K;
g 13K
- brownish-pink lepidolite image, 3K;
Lepidolite, Coolgardie, Western Australia, 1.661 mm thick
with Mn3+ in octahedral sites dominating the spectrum.
Data File:
cleavage 19K
- reddish-purple muscovite image, 10K;
Muscovite, GRR 727, Minas Gerais, Brazil, alurgite variety, 0.5 mm thick
with Mn3+ in octahedral sites dominating the spectrum.
Data Files:
a 38K;
b 38K;
g 31K
- pink muscovite image, 7K;
Muscovite, GRR 805, Harding Mine, New Mexico, USA, 2.0 mm thick.
Data Files:
a 13K;
b 13K;
g 13K
- orange-brown phlogopite image, 7K;
Phlogopite, GRR 728, Langban, Sweden, manganophyllite variety, 0.1 mm thick.
Data Files:
a 11K;
g 12K
Iron-containing micas
- medium-green phlogopite image, 7K;
Phlogopite, GRR 1575, Ontario, Canada, 1.897 mm thick, showing a typical Fe2+
absorption near 700 and 900 nm, and the OH overtone near 940 nm.
Data Files:
perpendicular to cleavage plane, 24K;
parallel to the cleavage plane, 24K
- red-brown phlogopite image, 7K;
Phlogopite, KB5-2, Kimberley, South Africa, with reverse pleochroism from
Fe3+ in the tetrahderal site, 0.03 mm thick. Reference: Farmer
and Boettcher (1981) Amer. Mineral 66, 1154-1163. Reverse pleochroism means
that the most intense absorption occurs when the electric vector of the incident
polarized light is parallel to the c-axis, opposite to the case for
most common micas.
Data Files:
a 11K;
b 16K
Chromium-containing micas
- green muscovite image, 4K;
Muscovite, GRR 1461, near Randsburg, Kern County, California, 0.493 mm thick,
showing typical Cr3+
absorption near 600 nm.
Data Files:
cleavage plane, 20K
- brown roscoelite image, 4K;
Roscoelite, GRR 1927, Stuckslager Mine, Coloma, El Dorado County, California, 0.040 mm thick,
showing Cr3+ absorption near 600 nm.
Data Files:
cleavage plane, 18K
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