Text Description: |
Blocks of vitrophyre in scree from Dome F at Site 4. Fine grained, holocrystalline, porphyritic with a matrix of cryptocrystalline material, feldspar, quartz?, opaque and alteration. Plagioclase phenocrysts (An34 - An38) are up to 4.0 mm and most are rounded; there is often strong oscillatory zoning. Opaque phenocrysts are up to 0.4 mm. There is an altered phase that is now an opaque rim with a core of unidentifiable high relief crystals ± plagioclase. A second altered phase, larger in size, consists of serpentine/chlorite and calcite. |