144 Microscopic Petrography – Cinder Cones and Associated Flows – Crater Peak

The Geology of Crater Lake National Park, Oregon With a reconnaissance of the Cascade Range southward to Mount Shasta by Howell Williams

Microscopic Petrography

 

Cinder Cones and Associated Flows

     Crater Peak

Among the analyzed ejecta of the parasitic cones in question are those of Crater Peak (no. 10). The specimen selected for analysis is typical of the scoriaceous ejecta (cinders) of this vent. It is an olivine-rich, hyalopilitic basaltic andesite. Approximately 45 per cent of the rock consists of deep-brown glass charged with dusty and granular ore. Approximately 30 per cent is composed of slender microliths of andesine. Zoned phenocrysts of labradorite, many with concentric inclusions of glass and thin, clear rims of andesine (5 per cent), fresh olivine crystals (8 per cent), granular augite (10 per cent), and accessory hypersthene (2 per cent) make up the remainder.

Several flows issued from the flanks of Crater Peak. Some are pale gray, massive, and almost holocrystalline; others are black, scoriaceous, and rich in glass. In different flows and even in different parts of a single flow, the proportion of the several ferromagnesian minerals varies considerably.

 

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