1. These rocks are mafic and often hypersthene , nepheline or quartz normative. 2. Augite-hypersthene andesite is the dominant rock type. 3. The andesitic lavas contain phenocrysts of andesine, hornblende, plagioclase and hypersthene . 4. Uturunku's lavas contain biotite, hypersthene , ilmenite, magnetite, orthopyroxene and plagioclase. 5. Augite, hypersthene and plagioclase are also present, with smaller contents of olivine and quartz. 6. The enstatite endmember has a positive optic sign, whereas bronzite and hypersthene both show a negative optic sign. 7. Dark brown varieties of augite and rhombic pyroxene ( hypersthene or bronzite ) have been observed but are not common. 8. The cleavage surfaces therefore exhibit a metallic sheen or schiller, which is even more pronounced in hypersthene than in bronzite. 9. Green augite and hypersthene form a considerable part of these rocks, they may contain also biotite, hornblende and quartz. 10. Ring Mountain, just north of Slag Hill, is a parasitic tuya composed of plagioclase-hypersthene -phyric andesite.
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