| Text Description: |
This is a coarse-grained, brown-yellow-beige, very lenticular, 5-8 cm tephra layer from near the base of the F-seam. The layer contains many coal fragments. Vague indications of possible lamina. About 30% plagioclase, 25% of altered feldspar and altered glass, 3-4% hornblende, and 2-3% opaques. Zoning is more prevalent than twinning in the plagioclase. The grains are angular to subrounded and there may be clay alteration along cleavages and in cracks. Trace apatite inclusions. The hornblende is moss-green with poor pleochroism. Trace quartz, volcanic rock fragments, unaltered glass, biotite, and zircon. |