| Text Description: |
Dome B at Site 5 that is surrounded by younger nA1 flows (94SJP51B). Fine grained, holocrystalline, seriate porphyritic with a matrix of cryptocrystalline material, opaque and plagioclase. Plagioclase phenocrysts (An36 - An52) are up to 1.75 mm and often have strong oscillatory zoning or normal zoning, and some have resorbed edges and occasional sieve textured zones. Amphibole phenocrysts are up to 1.05 mm with red-brown pleochroism and thick opaque and feldspar? rims; some grains are completely dehydrated. Opaque phenocrysts are mostly dehydrated amphibole, but primary opaque crystals are present up to 0.1 mm. 67.4% matrix, 24.3% plagioclase, 1.1% opaque, 4.7% altered amphibole, 0.1% alteration, 2.4% vesicles. |