Characterization of cation environments in polycrystalline forsterite by Mg-25 MAS, MQMAS, and QCPMG NMR
Forsterite (Mg2SiO4) is a silicate mineral frequently studied in the Earth sciences as it has a simple crystal structure and fast dissolution kinetics (elemental release rates under typical conditions on the order of 10-7 mol/m2/s1). During the dissolution process, spectroscopic techniques are often utilized to augment solution chemical analysis and to provide data for determining reaction mechanisms. Nuclear magnetic resonance (NMR) is able to interrogate the local bonding arrangement and coordination of a particular nuclide to obtain in structural information. Although previous NMR studies have focused on the silicon and oxygen environments in forsterite, studies focusing on the two nonequivalent magnesium environments in forsterite are limited to a few single-crystal studies. In this study, we present the results of 25Mg MAS, MQMAS, and static QCMG experiments performed on a powdered sample of pure synthetic forsterite. We also present spectral fits obtained from simulation software packages, which directly provide quadrupolar parameters for 25Mg nuclei occupying each of the two nonequivalent magnesium sites in the forsterite structure. These results are compared to calculations of the electric field gradient tenor conducted in previous ab initio studies to make definitive assignments correlating each peak to their respective magnesium site in the forsterite structure. Although previous NMR investigations of forsterite have focused on single-crystal samples, we have focused on powdered forsterite as the increased surface area of powdered samples makes them more amenable to laboratory-scale dissolution studies and, ultimately, the products from chemical weathering may be monitored an quantified.
- Research Organization:
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States). Environmental Molecular Sciences Lab. (EMSL)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 1000111
- Report Number(s):
- PNNL-SA-75288; AMMIAY; 25431; 400412000; TRN: US201024%%308
- Journal Information:
- American Mineralogist, 95(11-12):1601-1607, Vol. 95, Issue 11-12; ISSN 0003-004X
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BONDING
CATIONS
CHEMICAL ANALYSIS
CRYSTAL STRUCTURE
DISSOLUTION
ELECTRIC FIELDS
FOCUSING
ISOTOPES
KINETICS
MAGNESIUM
NUCLEAR MAGNETIC RESONANCE
NUCLEI
OXYGEN
REACTION KINETICS
SILICATE MINERALS
SILICON
SURFACE AREA
WEATHERING
Forsterite
magnesium
Mg-25
NMR
MQMAS
QCPMG
HIGH-RESOLUTION NMR
ANGLE-SPINNING NMR
INTEGER
QUADRUPOLAR NUCLEI
DISSOLUTION RATES
O-17 NMR
SPECTROSCOPY
SOLIDS
SENSITIVITY
OLIVINE
MG2SIO4
Environmental Molecular Sciences Laboratory