Mn-Mg disordering in cummingtonite: A high-temperature neutron powder diffraction study

J. J. Reece; S. A.T. Redfern; M. D. Welch; C. M.B. Henderson

doi:10.1180/002646100549166

Mn-Mg disordering in cummingtonite: A high-temperature neutron powder diffraction study

J. J. Reece^*, S. A.T. Redfern, M. D. Welch, C. M.B. Henderson

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

22 Citations (Scopus)

Abstract

The crystal structure of a manganoan cummingtonite, composition ([M4])(Na_0.13Ca_0.41Mg_0.46Mn_1.00) ([M1,2,3])(Mg_4.87Mn_0.13)[Si₈O₂₂](OH)₂, (Z = 2), a = 9.5539(2) Å, b = 18.0293(3) Å, c = 5.2999(1) Å, β = 102.614(2)°from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P2₁/m to C2/m phase transition, observed as spontaneous strains +ε₁ = -ε₂, occurs at ~107°C. Long-range disordering between Mg²⁺ and Mn²⁺ on the M(4) and M(2) sites occurs above 550°C. Mn²⁺ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6 ± 1.5 kJ mol^-1. Disordering induces an increase in X(Mn)(M2) and decrease in X(Mn)(M4) at elevated temperatures. Upon cooling, the ordered states of cation occupancy are 'frozen in' and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.

Original language	English
Pages (from-to)	255-266
Number of pages	12
Journal	Mineralogical Magazine
Volume	64
Issue number	2
DOIs	https://doi.org/10.1180/002646100549166
Publication status	Published - Apr 2000
Externally published	Yes

ASJC Scopus Subject Areas

Geochemistry and Petrology

Keywords

Cation partitioning
Cummingtonite
Neuytron diffraction
Order-disorder
Phase transition

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title = "Mn-Mg disordering in cummingtonite: A high-temperature neutron powder diffraction study",

abstract = "The crystal structure of a manganoan cummingtonite, composition ([M4])(Na0.13Ca0.41Mg0.46Mn1.00) ([M1,2,3])(Mg4.87Mn0.13)[Si8O22](OH)2, (Z = 2), a = 9.5539(2) {\AA}, b = 18.0293(3) {\AA}, c = 5.2999(1) {\AA}, β = 102.614(2)°from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P21/m to C2/m phase transition, observed as spontaneous strains +ε1 = -ε2, occurs at ~107°C. Long-range disordering between Mg2+ and Mn2+ on the M(4) and M(2) sites occurs above 550°C. Mn2+ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6 ± 1.5 kJ mol-1. Disordering induces an increase in X(Mn)(M2) and decrease in X(Mn)(M4) at elevated temperatures. Upon cooling, the ordered states of cation occupancy are 'frozen in' and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.",

keywords = "Cation partitioning, Cummingtonite, Neuytron diffraction, Order-disorder, Phase transition",

author = "Reece, {J. J.} and Redfern, {S. A.T.} and Welch, {M. D.} and Henderson, {C. M.B.}",

year = "2000",

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T2 - A high-temperature neutron powder diffraction study

AU - Reece, J. J.

AU - Redfern, S. A.T.

AU - Welch, M. D.

AU - Henderson, C. M.B.

PY - 2000/4

Y1 - 2000/4

N2 - The crystal structure of a manganoan cummingtonite, composition ([M4])(Na0.13Ca0.41Mg0.46Mn1.00) ([M1,2,3])(Mg4.87Mn0.13)[Si8O22](OH)2, (Z = 2), a = 9.5539(2) Å, b = 18.0293(3) Å, c = 5.2999(1) Å, β = 102.614(2)°from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P21/m to C2/m phase transition, observed as spontaneous strains +ε1 = -ε2, occurs at ~107°C. Long-range disordering between Mg2+ and Mn2+ on the M(4) and M(2) sites occurs above 550°C. Mn2+ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6 ± 1.5 kJ mol-1. Disordering induces an increase in X(Mn)(M2) and decrease in X(Mn)(M4) at elevated temperatures. Upon cooling, the ordered states of cation occupancy are 'frozen in' and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.

AB - The crystal structure of a manganoan cummingtonite, composition ([M4])(Na0.13Ca0.41Mg0.46Mn1.00) ([M1,2,3])(Mg4.87Mn0.13)[Si8O22](OH)2, (Z = 2), a = 9.5539(2) Å, b = 18.0293(3) Å, c = 5.2999(1) Å, β = 102.614(2)°from Talcville, New York, has been refined at high temperature using in situ neutron powder diffraction. The P21/m to C2/m phase transition, observed as spontaneous strains +ε1 = -ε2, occurs at ~107°C. Long-range disordering between Mg2+ and Mn2+ on the M(4) and M(2) sites occurs above 550°C. Mn2+ occupies the M(4) and M(2) sites preferring M(4) with a site-preference energy of 24.6 ± 1.5 kJ mol-1. Disordering induces an increase in X(Mn)(M2) and decrease in X(Mn)(M4) at elevated temperatures. Upon cooling, the ordered states of cation occupancy are 'frozen in' and strains in lattice parameters are maintained, suggesting that re-equilibration during cooling has not taken place.

KW - Cation partitioning

KW - Cummingtonite

KW - Neuytron diffraction

KW - Order-disorder

KW - Phase transition

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Mn-Mg disordering in cummingtonite: A high-temperature neutron powder diffraction study

Abstract

ASJC Scopus Subject Areas

Keywords

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