Silicate garnet: A micro to macroscopic (re)view
Abstract
Silicate garnets, general formula E3G2Si3O12, form an important class of rock-forming minerals and, in nature, most are solid solutions. Their crystal-chemical and solid-solution properties are sometimes interpreted in terms of the widely used Pyralspite-Ugrandite classification scheme, and this can lead to erroneous conclusions. In this study, published data are reviewed and analyzed to achieve a synthesis of relevant experimental and computational results and to construct a working “crystal-chemical model” for describing aluminosilicate garnet, E3Al2Si3O12, over different length scales. The pyrope-grossular (Py-Gr) solid solution is given special attention, because it has received a great deal of study. It also shows interesting crystal-chemical and thermodynamic mixing behavior. Computational and experimental investigations made on Py-Gr garnets indicate that the shorter Ca/Mg-O2 bond lengths appear to remain roughly constant in length across the binary and can be described as showing “Pauling limit-type” behavior. The longer Ca/Mg-O4 bonds behave differently, because they lengthen with increasing Gr component in the solid solution. Bond behavior in almandine-spessartine (Al-Sp) garnets appears to be partly different, because both Fe/Mn-O2 and Fe/ Mn-O4 bonds show “Pauling limit-type” behavior. E-O bond-length variations are continuous. The bonding type in all aluminosilicate garnet end-members is similar. An analysis shows that various computational simulations on Py-Gr solid solutions are consistent with each other with respect to E-O bond behavior and also with experimental IR, Raman, NMR spectroscopic, and X-ray diffraction results, but not completely with XAS studies made at the Ca edge. Ca/Mg-O4 bond behavior can be used to explain, partly, the nature of various micro/nanoscopic crystal-chemical and strain properties and macroscopic excess thermodynamic mixing behavior of Py-Gr garnets. Micro/nanostrain for the Py-Gr binary is asymmetric in nature, as are the various thermodynamic mixing functions ΔHex, ΔSex, and ΔVex. The widely cited Pyralspite-Ugrandite classification scheme has limited use in terms of explaining many physical and chemical properties of garnet and it should not be used to predict or describe, for example, solid-solution behavior.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Why is amazonitic K-feldspar an earmark of NYF-type granitic pegmatites? Clues from hybrid pegmatites in Madagascar
- Metamorphosed Ordovician Fe- and Mn-rich rocks in south-central Maine: From peri-Gondwanan deposition through Acadian metamorphism
- Boralsilite, Al16B6Si2O37, and “boron-mullite:” Compositional variations and associated phases in experiment and nature
- Prograde muscovite-rich pseudomorphs as indicators of conditions during metamorphism: An example from NW Maine
- Wagnerite in a cordierite-gedrite gneiss: Witness of long-term fluid-rock interaction in the continental crust (Ile d’Yeu, Armorican Massif, France)
- Mineral chemistry of Ti-rich biotite from pegmatite and metapelitic granulites of the Kerala Khondalite Belt (southeast India): Petrology and further insight into titanium substitutions
- Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control
- Proto-polymorphs of jimthompsonite and chesterite in contact-metamorphosed serpentinites from Japan
- Silicate garnet: A micro to macroscopic (re)view
- Monazite occurrence, chemistry, and chronology in the granitoid rocks of the Lachlan Fold Belt, Australia: An electron microprobe study
- Single-crystal 40Ar/39Ar age variation in muscovite of the Gassetts Schist and associated gneiss, Vermont Appalachians
- Single-crystal X-ray studies of trioctahedral micas coexisting with dioctahedral micas in metamorphic sequences from western Maine
- Tourmaline chemistry and the IIIB site
- The octahedral sheet of metamorphic 2M1-phengites: A combined EMPA and AXANES study
- Crystal chemistry of phlogopite from Vulture-S. Michele Subsynthem volcanic rocks (Mt. Vulture, Italy) and volcanological implications
- Beneath the Stillwater Complex: Petrology and geochemistry of quartz-plagioclasecordierite (or garnet)-orthopyroxene-biotite ± spinel hornfels, Mountain View area, Montana
- Correlation between crystallization pressure and structural parameters of phengites
- The modular structure of dovyrenite, Ca6Zr[Si2O7]2(OH)4: Alternate stacking of tobermorite and rosenbuschite-like units
- Environmental parameters affect the physical properties of fast-growing magnetosomes
- In situ Raman spectroscopy measurements of MgAl2O4 spinel up to 1400 °C
- Vibrational properties of δ-AlOOH under pressure
- Mössbauer spectroscopic study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O
- Rhönite in Luna 24 pyroxenes: First find from the Moon, and implications for volatiles in planetary magmas
- New high-pressure B2 phase of FeS above 180 GPa
- Magnesium K-edge EXAFS study of bond-length behavior in synthetic pyrope-grossular garnet solid solutions
Articles in the same Issue
- Why is amazonitic K-feldspar an earmark of NYF-type granitic pegmatites? Clues from hybrid pegmatites in Madagascar
- Metamorphosed Ordovician Fe- and Mn-rich rocks in south-central Maine: From peri-Gondwanan deposition through Acadian metamorphism
- Boralsilite, Al16B6Si2O37, and “boron-mullite:” Compositional variations and associated phases in experiment and nature
- Prograde muscovite-rich pseudomorphs as indicators of conditions during metamorphism: An example from NW Maine
- Wagnerite in a cordierite-gedrite gneiss: Witness of long-term fluid-rock interaction in the continental crust (Ile d’Yeu, Armorican Massif, France)
- Mineral chemistry of Ti-rich biotite from pegmatite and metapelitic granulites of the Kerala Khondalite Belt (southeast India): Petrology and further insight into titanium substitutions
- Multiple titanium substitutions in biotites from high-grade metapelitic xenoliths (Euganean Hills, Italy): Complete crystal chemistry and appraisal of petrologic control
- Proto-polymorphs of jimthompsonite and chesterite in contact-metamorphosed serpentinites from Japan
- Silicate garnet: A micro to macroscopic (re)view
- Monazite occurrence, chemistry, and chronology in the granitoid rocks of the Lachlan Fold Belt, Australia: An electron microprobe study
- Single-crystal 40Ar/39Ar age variation in muscovite of the Gassetts Schist and associated gneiss, Vermont Appalachians
- Single-crystal X-ray studies of trioctahedral micas coexisting with dioctahedral micas in metamorphic sequences from western Maine
- Tourmaline chemistry and the IIIB site
- The octahedral sheet of metamorphic 2M1-phengites: A combined EMPA and AXANES study
- Crystal chemistry of phlogopite from Vulture-S. Michele Subsynthem volcanic rocks (Mt. Vulture, Italy) and volcanological implications
- Beneath the Stillwater Complex: Petrology and geochemistry of quartz-plagioclasecordierite (or garnet)-orthopyroxene-biotite ± spinel hornfels, Mountain View area, Montana
- Correlation between crystallization pressure and structural parameters of phengites
- The modular structure of dovyrenite, Ca6Zr[Si2O7]2(OH)4: Alternate stacking of tobermorite and rosenbuschite-like units
- Environmental parameters affect the physical properties of fast-growing magnetosomes
- In situ Raman spectroscopy measurements of MgAl2O4 spinel up to 1400 °C
- Vibrational properties of δ-AlOOH under pressure
- Mössbauer spectroscopic study of synthetic leucophosphite, KFe2(PO4)2(OH)·2H2O
- Rhönite in Luna 24 pyroxenes: First find from the Moon, and implications for volatiles in planetary magmas
- New high-pressure B2 phase of FeS above 180 GPa
- Magnesium K-edge EXAFS study of bond-length behavior in synthetic pyrope-grossular garnet solid solutions
