File:Porphyritic rhyodacite (O'Leary Porphyry, Middle Pleistocene; O'Leary Peak, Arizona, USA) (27745649518).jpg
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| Description |
Porphyritic rhyodacite from the Pleistocene of Arizona, USA. (public display, Geology Department, Wittenberg University, Springfield, Ohio, USA) This volcanic lava sample comes from O'Leary Peak, a breached volcanic dome in Arizona's San Francisco Volcanic Field. It has a porphyritic texture, which refers to crystalline-textured igneous rocks having a mixture of large crystals (phenocrysts) and small crystals (groundmass). The light-colored, angular masses in the rock are feldspar phenocrysts. The feldspar is sanidine ((K,Na)AlSi3O8 - potassium sodium aluminosilicate). In some samples from this locality, the sanidine is rimmed with oligoclase feldspar ((Na,Ca)Al(Si,Al)Si2O8 - sodium calcium aluminosilicate). Other phenocrysts from this rock unit include quartz and oligoclase feldspar. Geologic unit: apparently derived from the "Purple Porphyry" of the O'Leary Porphyry, upper Middle Pleistocene, ~233 ka Locality: unrecorded/undisclosed site on O'Leary Peak, just north of Sunset Crater National Monument, ~26.5 air-kilometers north-northeast of Flagstaff, San Francisco Volcanic Field, north-central Arizona, USA (vicinity of 35° 24' 04.98" North latitude, 111° 31' 40.18" West longitude) |
| Date | |
| Source | Porphyritic rhyodacite (O'Leary Porphyry, Middle Pleistocene; O'Leary Peak, Arizona, USA) |
| Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/27745649518 (archive). It was reviewed on 24 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
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| Date/Time | Thumbnail | Dimensions | User | Comment | |
|---|---|---|---|---|---|
| current | 10:49, 24 November 2019 | | 2,752 × 1,315 (3.12 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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