| Text Description: |
Float boulder of silicic material at Site 1 in the Boyden Hills. Fine-grained, holocrystalline, porphyritic to glomeroporphyritic with a matrix of cryptocrystalline material, opaque and feldspar. Plagioclase phenocrysts (An55) are up to 1.88 mm and oscillatory zoning is common with less abundant normal zoning, grains occasionally have orthopyroxene or opaque inclusions. Orthopyroxene phenocrysts are up to 0.7 mm with intense pleochroism (birefringence is maximum for orthopyroxene), and frequently opaque inclusions are present. Amphibole phenocrysts are up to 1.3 mm with red-brown pleochroism and some have black coronas; occasionally grains have opaque inclusions; and some opaque aggregates may be dehydrated amphibole. Opaque phenocrysts are up to 0.3 mm. |