OH– in synthetic and natural coesite
-
Monika Koch-Müller
,
Przemyslaw Dera
Abstract
The incorporation of hydrogen into the coesite structure was investigated at pressures ranging from 4.0-9.0 GPa and temperatures from 750-1300 °C using Al and B doped SiO2 starting materials. The spectra show four sharp bands (ν1, ν2a, ν2b, and ν3) in the energy range of 3450-3580 cm-1, consistent with the hydrogarnet substitution [Si4+(T2) + 4O2- = vaT2 + 4OH-], two weak sharp bands at 3537 and 3500 cm-1 (v6a and ν6b) attributed to B-based point defects, and two weaker and broad bands at 3300 and 3210 cm-1 (ν4 and ν5) attributed to substitution of Si4+ by Al3+ + H. More than 80% of the dissolved water is incorporated via the hydrogarnet substitution mechanism. The hydrogen solubility in coesite increases with pressure and temperature. At 7.5 GPa and 1100 °C, 1335 H/106 Si is incorporated into the coesite structure. At 8.5 GPa and 1200 °C, the incorporation mechanism changes: in the IR spectra four new sharp bands appear in the energy range of 3380-3460 cm-1 (ν7-ν10) and the ν1-ν3 bands disappear. Single crystal X-ray diffraction, Raman spectroscopy, polarized single-crystal and in situ high-pressure FTIR spectroscopy confirm that the new bands are due to OH- in coesite. The polarization and high-pressure behavior of the ν7-ν10 OH bands is quite different from that of the ν1-ν3 bands, indicating that the H incorporation in coesite changes dramatically at these P and T conditions. Quantitative determination of hydrogen solubility in synthetic coesite as a function of pressure, temperature, and chemical impurity allow us to interpret observations in natural coesite. Hydrogen has not previously been detected in natural coesite samples from ultra high-pressure metamorphic rocks. In this study, we report the first FTIR spectrum of a natural OH-bearing coesite. The dominant substitution mechanism in this sample is the hydrogarnet substitution and the calculated hydrogen content is about 900 ζ ± 300 H/106 Si. The coesite occurs as an inclusion in diamond together with an OH-bearing omphacite. The shift of the OH-bands of coesite and omphacite to lower energies indicates that the minerals are still under confining pressure.
© 2015 by Walter de Gruyter Berlin/Boston
Abstract
The incorporation of hydrogen into the coesite structure was investigated at pressures ranging from 4.0-9.0 GPa and temperatures from 750-1300 °C using Al and B doped SiO2 starting materials. The spectra show four sharp bands (ν1, ν2a, ν2b, and ν3) in the energy range of 3450-3580 cm-1, consistent with the hydrogarnet substitution [Si4+(T2) + 4O2- = vaT2 + 4OH-], two weak sharp bands at 3537 and 3500 cm-1 (v6a and ν6b) attributed to B-based point defects, and two weaker and broad bands at 3300 and 3210 cm-1 (ν4 and ν5) attributed to substitution of Si4+ by Al3+ + H. More than 80% of the dissolved water is incorporated via the hydrogarnet substitution mechanism. The hydrogen solubility in coesite increases with pressure and temperature. At 7.5 GPa and 1100 °C, 1335 H/106 Si is incorporated into the coesite structure. At 8.5 GPa and 1200 °C, the incorporation mechanism changes: in the IR spectra four new sharp bands appear in the energy range of 3380-3460 cm-1 (ν7-ν10) and the ν1-ν3 bands disappear. Single crystal X-ray diffraction, Raman spectroscopy, polarized single-crystal and in situ high-pressure FTIR spectroscopy confirm that the new bands are due to OH- in coesite. The polarization and high-pressure behavior of the ν7-ν10 OH bands is quite different from that of the ν1-ν3 bands, indicating that the H incorporation in coesite changes dramatically at these P and T conditions. Quantitative determination of hydrogen solubility in synthetic coesite as a function of pressure, temperature, and chemical impurity allow us to interpret observations in natural coesite. Hydrogen has not previously been detected in natural coesite samples from ultra high-pressure metamorphic rocks. In this study, we report the first FTIR spectrum of a natural OH-bearing coesite. The dominant substitution mechanism in this sample is the hydrogarnet substitution and the calculated hydrogen content is about 900 ζ ± 300 H/106 Si. The coesite occurs as an inclusion in diamond together with an OH-bearing omphacite. The shift of the OH-bands of coesite and omphacite to lower energies indicates that the minerals are still under confining pressure.
© 2015 by Walter de Gruyter Berlin/Boston
Articles in the same Issue
- Structural systematics of hydrous ringwoodite and water in earth’s interior
- Compressibility of phase Egg AlSiO3OH: Equation of state and role of water at high pressure
- Synchrotron infrared spectroscopy of OH-chondrodite and OH-clinohumite at high pressure
- Structural deformation mechanisms of zeolites under pressure
- Variation of hydrogen bonded O···O distances in goethite at high pressure
- Pressure-controlled polytypism in hydrous layered materials
- OH– in synthetic and natural coesite
- Pressure-induced phase transformation of kalicinite (KHCO3) at 2.8 GPa and local structural changes around hydrogen atoms
- Potential docking sites and positions of hydrogen in high-pressure silicates
- Contrasting bonding behavior of two hydroxyl-bearing metamorphic minerals under pressure: Clinozoisite and topaz
- Experimental investigation of crystallization kinetics in a haplogranite system
- Assessment of cation substitutions along the gallium and fluorine analogue of the tremolite-glaucophane join
- Experimental hydrothermal alteration of partially metamict zircon
- On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion
- Ordering in spinels—A Monte Carlo study
- Single-crystal in situ high-temperature structural investigation of the I1̅ –I2/c phase transition in Ca0.2Sr0.8Al2Si2O8 feldspar
- New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho
- Fe and Ni impurities in synthetic diamond
- Phase transformations and reaction kinetics during the temperature-induced oxidation of natural olivine
- Thermal infrared spectroscopy and modeling of experimentally shocked plagioclase feldspars
- Oxygen isotopic composition of nano-scale uraninite at the Oklo-Okélobondo natural fission reactors, Gabon
- Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: Origin and evolution of garnet exsolution in clinopyroxene
- Letters. An assessment of nuclear microprobe analyses of B in silicate minerals
- Incommensurate phase in the kosmochlor-diopside join: A new polymorph of clinopyroxene
- Elastic properties of hydrous ringwoodite
- Thermochemistry of guest-free melanophlogite
- A simple model for the pressure preservation index of inclusions in diamond
Articles in the same Issue
- Structural systematics of hydrous ringwoodite and water in earth’s interior
- Compressibility of phase Egg AlSiO3OH: Equation of state and role of water at high pressure
- Synchrotron infrared spectroscopy of OH-chondrodite and OH-clinohumite at high pressure
- Structural deformation mechanisms of zeolites under pressure
- Variation of hydrogen bonded O···O distances in goethite at high pressure
- Pressure-controlled polytypism in hydrous layered materials
- OH– in synthetic and natural coesite
- Pressure-induced phase transformation of kalicinite (KHCO3) at 2.8 GPa and local structural changes around hydrogen atoms
- Potential docking sites and positions of hydrogen in high-pressure silicates
- Contrasting bonding behavior of two hydroxyl-bearing metamorphic minerals under pressure: Clinozoisite and topaz
- Experimental investigation of crystallization kinetics in a haplogranite system
- Assessment of cation substitutions along the gallium and fluorine analogue of the tremolite-glaucophane join
- Experimental hydrothermal alteration of partially metamict zircon
- On the origin of size-dependent and size-independent crystal growth: Influence of advection and diffusion
- Ordering in spinels—A Monte Carlo study
- Single-crystal in situ high-temperature structural investigation of the I1̅ –I2/c phase transition in Ca0.2Sr0.8Al2Si2O8 feldspar
- New clinopyroxene-liquid thermobarometers for mafic, evolved, and volatile-bearing lava compositions, with applications to lavas from Tibet and the Snake River Plain, Idaho
- Fe and Ni impurities in synthetic diamond
- Phase transformations and reaction kinetics during the temperature-induced oxidation of natural olivine
- Thermal infrared spectroscopy and modeling of experimentally shocked plagioclase feldspars
- Oxygen isotopic composition of nano-scale uraninite at the Oklo-Okélobondo natural fission reactors, Gabon
- Clinopyroxenite from the Sulu ultrahigh-pressure terrane, eastern China: Origin and evolution of garnet exsolution in clinopyroxene
- Letters. An assessment of nuclear microprobe analyses of B in silicate minerals
- Incommensurate phase in the kosmochlor-diopside join: A new polymorph of clinopyroxene
- Elastic properties of hydrous ringwoodite
- Thermochemistry of guest-free melanophlogite
- A simple model for the pressure preservation index of inclusions in diamond
