Crystal structure and Raman spectrum of a high-pressure Li-rich majoritic garnet, (Li2Mg)Si2(SiO4)3

Hexiong Yang, Jürgen Konzett, Robert T Downs, Daniel J. Frost

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

A Li-rich majoritic garnet (LiMGt), (Li2Mg)Si 2(SiO4)3, was synthesized at 15 GPa and 1500 °C and its structure studied with single-crystal X-ray diffraction and Raman spectroscopy. It is cubic with space group Ia3̄Bd and unit-cell parameters a = 11.2660(2) å and V = 1429.91(1) å3. The 8-, 6-, and 4-coordinated cation sites in LiMGt are occupied by (Li+ + Mg 2+), Si4+, and Si4+, respectively. Whereas the SiO6 octahedron is nearly regular, the XO8 dodecahedron is the most distorted of all known silicate garnets in terms of the bond-length distortion index. All Raman peaks of LiMGt are broader than those of pyrope, due to the substitution of Li+ for Mg2+ at the dodecahedral site. Furthermore, both Si-O symmetric stretching (A1g-v1) and O-Si-O symmetric bending (A1g-v2) modes of LiMGt shift significantly to higher frequencies relative to the corresponding ones of pyrope. In contrast, the A1g-(SiO4) rotational mode of LiMGt displays a much lower frequency than that of pyrope. This study represents the first structural report on a garnet with an all-silicate framework and suggests that, like Na incorporation in garnets, the pressure-dependent coupled substitution of (Li+ + Si4+) for (Mg2+ + Al3+) is likely one of the primary mechanisms for Li enrichment in garnets in the mantle and the transition zone.

Original languageEnglish (US)
Pages (from-to)630-633
Number of pages4
JournalAmerican Mineralogist
Volume94
Issue number4
DOIs
StatePublished - Apr 2009

Fingerprint

Garnets
crystal structure
garnets
Raman scattering
garnet
Crystal structure
Raman spectra
pyrope
Silicates
silicates
substitution
Substitution reactions
tectosilicate
substitutes
Bond length
Raman spectroscopy
transition zone
Stretching
Cations
Earth mantle

Keywords

  • Crystal structure
  • High pressure
  • Majoritic garnet
  • Raman spectroscopy

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Crystal structure and Raman spectrum of a high-pressure Li-rich majoritic garnet, (Li2Mg)Si2(SiO4)3. / Yang, Hexiong; Konzett, Jürgen; Downs, Robert T; Frost, Daniel J.

In: American Mineralogist, Vol. 94, No. 4, 04.2009, p. 630-633.

Research output: Contribution to journalArticle

Yang, Hexiong ; Konzett, Jürgen ; Downs, Robert T ; Frost, Daniel J. / Crystal structure and Raman spectrum of a high-pressure Li-rich majoritic garnet, (Li2Mg)Si2(SiO4)3. In: American Mineralogist. 2009 ; Vol. 94, No. 4. pp. 630-633.
@article{e3de8a6b5ff34fedb2e6b75db1d1ffa3,
title = "Crystal structure and Raman spectrum of a high-pressure Li-rich majoritic garnet, (Li2Mg)Si2(SiO4)3",
abstract = "A Li-rich majoritic garnet (LiMGt), (Li2Mg)Si 2(SiO4)3, was synthesized at 15 GPa and 1500 °C and its structure studied with single-crystal X-ray diffraction and Raman spectroscopy. It is cubic with space group Ia3̄Bd and unit-cell parameters a = 11.2660(2) {\aa} and V = 1429.91(1) {\aa}3. The 8-, 6-, and 4-coordinated cation sites in LiMGt are occupied by (Li+ + Mg 2+), Si4+, and Si4+, respectively. Whereas the SiO6 octahedron is nearly regular, the XO8 dodecahedron is the most distorted of all known silicate garnets in terms of the bond-length distortion index. All Raman peaks of LiMGt are broader than those of pyrope, due to the substitution of Li+ for Mg2+ at the dodecahedral site. Furthermore, both Si-O symmetric stretching (A1g-v1) and O-Si-O symmetric bending (A1g-v2) modes of LiMGt shift significantly to higher frequencies relative to the corresponding ones of pyrope. In contrast, the A1g-(SiO4) rotational mode of LiMGt displays a much lower frequency than that of pyrope. This study represents the first structural report on a garnet with an all-silicate framework and suggests that, like Na incorporation in garnets, the pressure-dependent coupled substitution of (Li+ + Si4+) for (Mg2+ + Al3+) is likely one of the primary mechanisms for Li enrichment in garnets in the mantle and the transition zone.",
keywords = "Crystal structure, High pressure, Majoritic garnet, Raman spectroscopy",
author = "Hexiong Yang and J{\"u}rgen Konzett and Downs, {Robert T} and Frost, {Daniel J.}",
year = "2009",
month = "4",
doi = "10.2138/am.2009.3144",
language = "English (US)",
volume = "94",
pages = "630--633",
journal = "American Mineralogist",
issn = "0003-004X",
publisher = "Mineralogical Society of America",
number = "4",

}

TY - JOUR

T1 - Crystal structure and Raman spectrum of a high-pressure Li-rich majoritic garnet, (Li2Mg)Si2(SiO4)3

AU - Yang, Hexiong

AU - Konzett, Jürgen

AU - Downs, Robert T

AU - Frost, Daniel J.

PY - 2009/4

Y1 - 2009/4

N2 - A Li-rich majoritic garnet (LiMGt), (Li2Mg)Si 2(SiO4)3, was synthesized at 15 GPa and 1500 °C and its structure studied with single-crystal X-ray diffraction and Raman spectroscopy. It is cubic with space group Ia3̄Bd and unit-cell parameters a = 11.2660(2) å and V = 1429.91(1) å3. The 8-, 6-, and 4-coordinated cation sites in LiMGt are occupied by (Li+ + Mg 2+), Si4+, and Si4+, respectively. Whereas the SiO6 octahedron is nearly regular, the XO8 dodecahedron is the most distorted of all known silicate garnets in terms of the bond-length distortion index. All Raman peaks of LiMGt are broader than those of pyrope, due to the substitution of Li+ for Mg2+ at the dodecahedral site. Furthermore, both Si-O symmetric stretching (A1g-v1) and O-Si-O symmetric bending (A1g-v2) modes of LiMGt shift significantly to higher frequencies relative to the corresponding ones of pyrope. In contrast, the A1g-(SiO4) rotational mode of LiMGt displays a much lower frequency than that of pyrope. This study represents the first structural report on a garnet with an all-silicate framework and suggests that, like Na incorporation in garnets, the pressure-dependent coupled substitution of (Li+ + Si4+) for (Mg2+ + Al3+) is likely one of the primary mechanisms for Li enrichment in garnets in the mantle and the transition zone.

AB - A Li-rich majoritic garnet (LiMGt), (Li2Mg)Si 2(SiO4)3, was synthesized at 15 GPa and 1500 °C and its structure studied with single-crystal X-ray diffraction and Raman spectroscopy. It is cubic with space group Ia3̄Bd and unit-cell parameters a = 11.2660(2) å and V = 1429.91(1) å3. The 8-, 6-, and 4-coordinated cation sites in LiMGt are occupied by (Li+ + Mg 2+), Si4+, and Si4+, respectively. Whereas the SiO6 octahedron is nearly regular, the XO8 dodecahedron is the most distorted of all known silicate garnets in terms of the bond-length distortion index. All Raman peaks of LiMGt are broader than those of pyrope, due to the substitution of Li+ for Mg2+ at the dodecahedral site. Furthermore, both Si-O symmetric stretching (A1g-v1) and O-Si-O symmetric bending (A1g-v2) modes of LiMGt shift significantly to higher frequencies relative to the corresponding ones of pyrope. In contrast, the A1g-(SiO4) rotational mode of LiMGt displays a much lower frequency than that of pyrope. This study represents the first structural report on a garnet with an all-silicate framework and suggests that, like Na incorporation in garnets, the pressure-dependent coupled substitution of (Li+ + Si4+) for (Mg2+ + Al3+) is likely one of the primary mechanisms for Li enrichment in garnets in the mantle and the transition zone.

KW - Crystal structure

KW - High pressure

KW - Majoritic garnet

KW - Raman spectroscopy

UR - http://www.scopus.com/inward/record.url?scp=67650300234&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=67650300234&partnerID=8YFLogxK

U2 - 10.2138/am.2009.3144

DO - 10.2138/am.2009.3144

M3 - Article

AN - SCOPUS:67650300234

VL - 94

SP - 630

EP - 633

JO - American Mineralogist

JF - American Mineralogist

SN - 0003-004X

IS - 4

ER -