147 Microscopic Petrography – Cinder Cones and Associated Flows – Desert Cone and Bald Crater

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

     Desert Cone and Bald Crater

The scoriaceous bombs and lapilli, as well as the lavas, erupted from Desert Cone are invariably rich in porphyritic olivine (5 to 10 per cent). In fact, they include the most olivine-rich flows within the Park. No chemical analyses are available, but the majority of the products of this vent are probably true basalts and the remainder are transitional toward basic andesites. In general, as might be anticipated, the pyroclastic ejecta contain more glass than the flows, some of which are holocrystalline and intergranular. Where the lavas and fragmental ejecta have been reddened by gas action, the olivine is commonly replaced in large part by granular ore and hematite.

 

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