| Text Description: |
A rubbly outcrop of silicic dike cutting through andesite at Site 12. Fine grained, holocrystalline, seriate porphyritic with a matrix of opaque, plagioclase, quartz?, cryptocrystalline material and minor alteration patches. Plagioclase phenocrysts (An28 - An47) are up to 1.75 mm and are commonly oscillatory zoned; the largest grains tend to be sieve textured. Orthopyroxene phenocrysts are up to 0.8 mm and strongly pleochroic; some have opaque inclusions. Amphibole phenocrysts are up to 0.8 mm with green-yellow pleochroism, and frequently include small opaque crystals along rim. Opaque phenocrysts are up to 0.3 mm. 62.0% matrix, 29.6% plagioclase, 2.8% orthopyroxene, 0.7% opaque, 0.3% amphibole, 4.6% vesicles. |