Abstract
Exsolution rods of relict coesite together with quartz were identified in omphacite in eclogites from western Tianshan, China. They are oriented along the c-axis of the host clinopyroxenes and have grain size up to 30 μm long and 2-3 μm wide. Raman spectra of exsolved lamellae yield consistent but weak bands at 521, 270, 181, 151, and 118 cm - 1 , typical for coesite, in addition to those of quartz and the host omphacite. Such occurrences together with textured observations suggest a two-stage evolution of SiO 2 exsolution rods in omphacite. Lamellae of coesite were apparently exsolved from supersilicic omphacite at P 5.0 GPa and the transformation from coesite to quartz occurred during retrograde metamorphism.
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