Moessbauer spectra of biotite from metapelites

Journal Article · · American Mineralogist; (USA)

OSTI ID:6258729

Dyar, M D ^[1]

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1. Univ. of Oregon, Eugene (USA)

Moessbauer spectra of 52 biotite samples from metapelites of the Rangeley, Oquossoc, and Bryant Pond Quadrangles of northwestern Maine are examined to evaluate the oxidation state and site occupancies of Fe atoms. Spectra show nearly invariant peak positions for the cis-M2 site ({delta} = 1.13 mm/s and {Delta} = 2.60 mm/s) in the octahedral sheet of the biotite but greater variation in Fe{sup 2+} trans-M1 doublets ({delta} 1.13 mm/s and {Delta} = 1.95-2.60 mm/s), which reflects a range of distortion in that site. Tetrahedral Fe{sup 3+} is present in amounts ranging from 4-14% of the total iron in all samples studied, roughly equivalent to the number of octahedral vacancies. Two octahedral Fe{sup 3+} doublets can be resolved in spectra for samples from the more oxidized assemblages studied. In more reduced rocks these doublets are poorly resolved and can be best represented by a single doublet with averaged hyperfine parameters. Fe{sup 3+}/{Sigma}Fe remains constant within analytical errors among samples from lower garnet to potassium feldspar + sillimanite metamorphic grades as long as the oxide mineral phase does not change. However, octahedral Fe{sup 3+} content increases from a baseline of 4% of the total Fe in graphite-ilmenite-bearing assemblages up to 40% in biotites from hematite-bearing assemblages. The octahedral Fe{sup 2+} M2/M1 ratio that reflects ordering typically falls in a range from 2 to 3.5, but extremes of 1.14 up to 5.20 are observed in samples from sulfide-bearing or highly-oxidized assemblages.

• OSTI ID: 6258729
• Journal Information: American Mineralogist; (USA), Journal Name: American Mineralogist; (USA) Vol. 75:5-6; ISSN AMMIA; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360602 -- Other Materials-- Structure & Phase Studies
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
58 GEOSCIENCES
580000 -- Geosciences
BIOTITE
CHEMICAL REACTIONS
CHEMISTRY
CRYSTAL STRUCTURE
ELEMENTS
FEDERAL REGION I
GEOCHEMISTRY
GEOLOGIC DEPOSITS
IRON
MAINE
METALS
MICA
MINERALS
MOESSBAUER EFFECT
NORTH AMERICA
OXIDATION
SILICATE MINERALS
SPECTROSCOPY
TRANSITION ELEMENTS
USA
VALENCE
VARIATIONS