File:Olivine basalt (Pleistocene; lava flow near Keeler, California, USA) (16540711697).jpg
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Summary
[edit]DescriptionOlivine basalt (Pleistocene; lava flow near Keeler, California, USA) (16540711697).jpg |
Olivine porphyritic basalt from the Pleistocene of California, USA. (4.0 cm across at its widest) Igneous rocks form by the cooling & crystallization of hot, molten rock (magma & lava). If this happens at or near the land surface, or on the seafloor, they are extrusive igneous rocks. If this happens deep underground, they are intrusive igneous rocks. Most igneous rocks have a crystalline texture, but some are clastic, vesicular, frothy, or glassy. Basalt is a common extrusive igneous rock. Basalt is the dominant rock in Earth’s upper oceanic crust. Black lava rocks seen at famous volcanoes such as Mt. Kilauea in Hawaii and Mt. Etna in Sicily are composed of basalt. Basalt has a mafic chemistry. Mafic igneous rocks are generally dark-colored, have 45-52% silica (= SiO2 chemistry) (mafic has also been defined as 45 to 55% silica), are rich in iron (Fe), magnesium (Mg), & calcium (Ca), and are dominated by the minerals plagioclase feldspar and pyroxene. Many basalts have an aphanitic texture (finely crystalline; all or almost all crystals are <1 mm in size). Porphyritic basalt (see above photo) has the same chemistry & mineralogy as ordinary basalt, but differs in the size range of its crystals. Porphyritic basalts have a mix of large & small crystals. Large crystals in a porphyritic rock are called phenocrysts. The smaller crystals make up the groundmass. The above sample is an olivine porphyritic basalt. The greenish-yellow crystals are olivine phenocrysts ((Mg,Fe)2SiO4). The dark-colored material is plagioclase feldspar and pyroxene. This rock apparently comes from a Pleistocene lava flow (likely "Qb" of Stinson, 1977 - Geologic Map of the Keeler 15' Quadrangle, Inyo County, California). Locality: unrecorded site near Keeler, western Inyo County, eastern California, USA (but probably from a roadcut or roadside outcrop along Rt. 190 southeast of Keeler, ~5 to 7 km southeast of the Rt. 136-Rt. 190 intersection) |
Date | |
Source | Olivine basalt (Pleistocene; lava flow near Keeler, California, 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@N05/16540711697 (archive). It was reviewed on 10 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
10 October 2019
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Date/Time | Thumbnail | Dimensions | User | Comment | |
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current | 00:15, 10 October 2019 | 1,315 × 1,110 (2.66 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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Pixel composition | RGB |
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Orientation | Normal |
Horizontal resolution | 800 dpi |
Vertical resolution | 800 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 19:43, 7 March 2015 |
Color space | Uncalibrated |
Image width | 1,315 px |
Image height | 1,110 px |
Date and time of digitizing | 14:38, 7 March 2015 |
Date metadata was last modified | 14:43, 7 March 2015 |