Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca

A. M. Hofmeister, Timothy Jay Fagan, K. M. Campbell, R. B. Schaal

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

Mg2+-Fe2+ substitution in the dodecahedral interstice of eight natural single crystals and two synthetic polycrystalline garnets was investigated by measurement of mid- and far-infrared (IR) reflectance spectra across the pyrope-almandine [Py-Al = (Mgx-Fe1-x)3Al2Si3O 12] binary. The effect of minor Mn and Ca substitution was investigated by comparison with spectra of four additional natural garnets, Py8Al82Sp10 and Py10Al76Sp14, where Sp denotes spessartine (Mn3Al2Si3O12), and Py72Al18Gr10 and Py54Al36Gr10, where Gr denotes grossular (Ca3Al2Si3O12). Data obtained from the two synthetic polycrystals are in excellent agreement with data from the single crystals. Frequencies of all 17 IR-active fundamental modes were observed in all specimens except pyrope. Of the 17 modes, 16 show linear correlations between frequency and composition along the pyrope-almandine join. The remaining mode, assigned to translations of the divalent cations against the O framework, exhibits two-mode behavior. The trends show that two modes in pyrope are accidentally degenerate. Frequencies of garnets with up to 10 mol% spessartine and grossular contents lie on the trends defined by the pyrope-almandine samples with negligible impurities. However, one to three additional modes are seen for some intermediate compositions, apparently resulting from either resonances among combination modes or two-mode behavior due to high Ca contents. The nearly linear behavior of the modes indicates that mixing should be close to ideal for the pyrope-almandine series because the lattice contribution dominates heat capacity, entropy, and compressibility.

Original languageEnglish
Pages (from-to)418-428
Number of pages11
JournalAmerican Mineralogist
Volume81
Issue number3-4
Publication statusPublished - 1996 Mar
Externally publishedYes

Fingerprint

almandine
pyrope
Garnets
infrared spectroscopy
garnets
Infrared spectroscopy
garnet
Single crystals
crystal
single crystals
Substitution reactions
Infrared radiation
spessartine
grossular
Divalent Cations
Polycrystals
Chemical analysis
Compressibility
Specific heat
substitution

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca. / Hofmeister, A. M.; Fagan, Timothy Jay; Campbell, K. M.; Schaal, R. B.

In: American Mineralogist, Vol. 81, No. 3-4, 03.1996, p. 418-428.

Research output: Contribution to journalArticle

Hofmeister, AM, Fagan, TJ, Campbell, KM & Schaal, RB 1996, 'Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca', American Mineralogist, vol. 81, no. 3-4, pp. 418-428.
Hofmeister, A. M. ; Fagan, Timothy Jay ; Campbell, K. M. ; Schaal, R. B. / Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca. In: American Mineralogist. 1996 ; Vol. 81, No. 3-4. pp. 418-428.
@article{8270eb63f8e2416f8dc4c95f528cde51,
title = "Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca",
abstract = "Mg2+-Fe2+ substitution in the dodecahedral interstice of eight natural single crystals and two synthetic polycrystalline garnets was investigated by measurement of mid- and far-infrared (IR) reflectance spectra across the pyrope-almandine [Py-Al = (Mgx-Fe1-x)3Al2Si3O 12] binary. The effect of minor Mn and Ca substitution was investigated by comparison with spectra of four additional natural garnets, Py8Al82Sp10 and Py10Al76Sp14, where Sp denotes spessartine (Mn3Al2Si3O12), and Py72Al18Gr10 and Py54Al36Gr10, where Gr denotes grossular (Ca3Al2Si3O12). Data obtained from the two synthetic polycrystals are in excellent agreement with data from the single crystals. Frequencies of all 17 IR-active fundamental modes were observed in all specimens except pyrope. Of the 17 modes, 16 show linear correlations between frequency and composition along the pyrope-almandine join. The remaining mode, assigned to translations of the divalent cations against the O framework, exhibits two-mode behavior. The trends show that two modes in pyrope are accidentally degenerate. Frequencies of garnets with up to 10 mol{\%} spessartine and grossular contents lie on the trends defined by the pyrope-almandine samples with negligible impurities. However, one to three additional modes are seen for some intermediate compositions, apparently resulting from either resonances among combination modes or two-mode behavior due to high Ca contents. The nearly linear behavior of the modes indicates that mixing should be close to ideal for the pyrope-almandine series because the lattice contribution dominates heat capacity, entropy, and compressibility.",
author = "Hofmeister, {A. M.} and Fagan, {Timothy Jay} and Campbell, {K. M.} and Schaal, {R. B.}",
year = "1996",
month = "3",
language = "English",
volume = "81",
pages = "418--428",
journal = "American Mineralogist",
issn = "0003-004X",
publisher = "Mineralogical Society of America",
number = "3-4",

}

TY - JOUR

T1 - Single-crystal IR spectroscopy of pyrope-almandine garnets with minor amounts of Mn and Ca

AU - Hofmeister, A. M.

AU - Fagan, Timothy Jay

AU - Campbell, K. M.

AU - Schaal, R. B.

PY - 1996/3

Y1 - 1996/3

N2 - Mg2+-Fe2+ substitution in the dodecahedral interstice of eight natural single crystals and two synthetic polycrystalline garnets was investigated by measurement of mid- and far-infrared (IR) reflectance spectra across the pyrope-almandine [Py-Al = (Mgx-Fe1-x)3Al2Si3O 12] binary. The effect of minor Mn and Ca substitution was investigated by comparison with spectra of four additional natural garnets, Py8Al82Sp10 and Py10Al76Sp14, where Sp denotes spessartine (Mn3Al2Si3O12), and Py72Al18Gr10 and Py54Al36Gr10, where Gr denotes grossular (Ca3Al2Si3O12). Data obtained from the two synthetic polycrystals are in excellent agreement with data from the single crystals. Frequencies of all 17 IR-active fundamental modes were observed in all specimens except pyrope. Of the 17 modes, 16 show linear correlations between frequency and composition along the pyrope-almandine join. The remaining mode, assigned to translations of the divalent cations against the O framework, exhibits two-mode behavior. The trends show that two modes in pyrope are accidentally degenerate. Frequencies of garnets with up to 10 mol% spessartine and grossular contents lie on the trends defined by the pyrope-almandine samples with negligible impurities. However, one to three additional modes are seen for some intermediate compositions, apparently resulting from either resonances among combination modes or two-mode behavior due to high Ca contents. The nearly linear behavior of the modes indicates that mixing should be close to ideal for the pyrope-almandine series because the lattice contribution dominates heat capacity, entropy, and compressibility.

AB - Mg2+-Fe2+ substitution in the dodecahedral interstice of eight natural single crystals and two synthetic polycrystalline garnets was investigated by measurement of mid- and far-infrared (IR) reflectance spectra across the pyrope-almandine [Py-Al = (Mgx-Fe1-x)3Al2Si3O 12] binary. The effect of minor Mn and Ca substitution was investigated by comparison with spectra of four additional natural garnets, Py8Al82Sp10 and Py10Al76Sp14, where Sp denotes spessartine (Mn3Al2Si3O12), and Py72Al18Gr10 and Py54Al36Gr10, where Gr denotes grossular (Ca3Al2Si3O12). Data obtained from the two synthetic polycrystals are in excellent agreement with data from the single crystals. Frequencies of all 17 IR-active fundamental modes were observed in all specimens except pyrope. Of the 17 modes, 16 show linear correlations between frequency and composition along the pyrope-almandine join. The remaining mode, assigned to translations of the divalent cations against the O framework, exhibits two-mode behavior. The trends show that two modes in pyrope are accidentally degenerate. Frequencies of garnets with up to 10 mol% spessartine and grossular contents lie on the trends defined by the pyrope-almandine samples with negligible impurities. However, one to three additional modes are seen for some intermediate compositions, apparently resulting from either resonances among combination modes or two-mode behavior due to high Ca contents. The nearly linear behavior of the modes indicates that mixing should be close to ideal for the pyrope-almandine series because the lattice contribution dominates heat capacity, entropy, and compressibility.

UR - http://www.scopus.com/inward/record.url?scp=0029768608&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0029768608&partnerID=8YFLogxK

M3 - Article

AN - SCOPUS:0029768608

VL - 81

SP - 418

EP - 428

JO - American Mineralogist

JF - American Mineralogist

SN - 0003-004X

IS - 3-4

ER -