| Text Description: |
Silicic flow from Dome A at Site 5. Sample is from the upper vitrophyre. Fine-grained vitrophyre, hypocrystalline, intersertal, locally pilotaxitic, seriate porphyritic with a matrix of colorless glass, feldspar, biotite, amphibole? and opaque. Plagioclase phenocrysts are up to 1.75 mm. There is also untwinned or sanidine twinned feldspar and a few have resorbed cores with overgrowth rims. Biotite phenocrysts are up to 0.6 mm. Opaque phenocrysts are up to 0.25 mm. Zircon phenocrysts are ~0.075 mm. 96.1% matrix, 3.7% plagioclase, 0.2% biotite. |