File:Phenotrachytic welded tuff (Wall Mountain Tuff, Middle Eocene, 36.73 Ma; Teller County, Colorado, USA) 2 (31674554366).jpg
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Summary[edit]
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| Description |
Phenotrachytic welded tuff from the Eocene of Teller County, central Colorado, USA. (7.7 cm across at its widest) Volcanic tuff is a fine-grained, clastic-textured, extrusive igneous rock. It forms by lithification of loose volcanic materials produced by an explosive eruption. Some volcanic deposits remain so hot after deposition that they self-lithify - the fragments become "welded" together. Shown above is a welded tuff from the Tertiary of central Colorado. It is composed of fine-grained ash plus some larger grains of pumice, volcanic glass, rock fragments, and various phenocrysts (sanidine feldspar, plagioclase feldspar, biotite mica, clinopyroxene, and hornblende amphibole). Published chemical analysis has shown that this rock is felsic and alkaline (calc-alkaline rhyolitic welded tuff). Petrologically, this makes is a phenotrachytic welded tuff. The source volcano was located near Mt. Princeton in the Sawatch Range, over 50 miles away from the outcrop. Stratigraphy: Wall Mountain Tuff, Upper Eocene, 36.73 Ma |
| Date | |
| Source | Phenotrachytic welded tuff (Wall Mountain Tuff, Middle Eocene, 36.73 Ma; Teller County, Colorado, USA) 2 |
| 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@N05/31674554366 (archive). It was reviewed on 6 December 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 | 02:02, 6 December 2019 | | 3,331 × 1,812 (4.18 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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