Unpolarized Raman spectra of quartz were obtained on a JY Horiba LabRAM HR800 Raman microprobe at Virginia Tech, using a high-resolution 800 mm focal-length spectrometer with 1800 lines/mm grating and a 100mW 514.57 nm argon laser. We used a 40x objective with a confocal aperture of 400 and a 150 μm slit width. The spectra were centered at 360 cm-1 (range of 73.8-633.1 cm-1) to allow simultaneous collection of the three main quartz peaks (~464, 206 and 127 cm-1 at ambient conditions) and three Ar plasma lines (520.30, 266.29 and 116.04 cm-1), for drift correction. The Sifnos sample was analyzed using a 600 lines/mm grating (spectral
High-pressure (0.8 gigapascals) granulite facies garnet from Gore Mountain, New York, hosts multiple solid inclusions containing the low-pressure silica polymorph cristobalite along with albite and minor ilmenite. Identification of cristobalite is based on Raman spectra, electron microprobe analysis, and microthermometric measurements on the alpha/beta phase transformation. The cristobalite plus albite inclusions may have originated as small, trapped samples of hydrous sodium-aluminum-siliceous melt. Diffusive loss of water from these inclusions under isothermal, isochoric conditions may have resulted in a large enough internal pressure decrease to promote the metastable crystallization of cristobalite.
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