File:Pegmatitic granite (alaskite) 2 (16127154743).jpg
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Summary
[edit]DescriptionPegmatitic granite (alaskite) 2 (16127154743).jpg |
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. Granite is a common intrusive igneous rock. Garden-variety granites are composed of quartz, potassium feldspar (K-feldspar), sodic plagioclase feldspar, hornblende amphibole, and mica. Granites have a felsic chemistry. Felsic igneous rocks are generally light-colored, have >65% silica (“silica” = SiO2 chemistry) (felsic has also been defined as >70% silica), are rich in potassium (K) & sodium (Na), and are dominated by the minerals quartz and K-feldspar. The granite specimen shown above has a pegmatitic texture (many granites have a phaneritic texture, with crystals between 1 mm and 1 cm in size each). All or almost all of the crystals in a pegmatitic rock are >1 cm in size each. Pegmatitic granite usually forms by cooling of a relatively water-rich magma. Very slow cooling of magma can also result in a pegmatitic texture. This pegmatitic granite has such a low ferromagnesian mineral content that it appears to consist only of quartz and potassium feldspar - such granites are called alaskites. Whitish, glassy crystals = quartz Pale pinkish-cream colored crystals at upper left = potassium feldspar |
Date | |
Source | Pegmatitic granite (alaskite) 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@N05/16127154743 (archive). It was reviewed on 12 November 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
12 November 2019
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current | 04:15, 12 November 2019 | ![]() | 3,996 × 2,860 (2.67 MB) | Ser Amantio di Nicolao (talk | contribs) | Transferred from Flickr via #flickr2commons |
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot D10 |
Exposure time | 1/80 sec (0.0125) |
F-number | f/4.5 |
ISO speed rating | 320 |
Date and time of data generation | 10:18, 18 February 2013 |
Lens focal length | 14.303 mm |
Orientation | Normal |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop CS2 Macintosh |
File change date and time | 18:39, 7 March 2015 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 10:18, 18 February 2013 |
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APEX shutter speed | 6.3125 |
APEX aperture | 4.34375 |
APEX exposure bias | −0.33333333333333 |
Maximum land aperture | 4.34375 APEX (f/4.51) |
Metering mode | Pattern |
Flash | Flash did not fire, auto mode |
Supported Flashpix version | 1 |
Color space | sRGB |
Focal plane X resolution | 16,460.905349794 |
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Focal plane resolution unit | inches |
Sensing method | One-chip color area sensor |
File source | Digital still camera |
Custom image processing | Normal process |
Exposure mode | Manual exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Standard |
Supported Flashpix version | 1 |
Image width | 3,996 px |
Image height | 2,860 px |
Date metadata was last modified | 13:39, 7 March 2015 |
IIM version | 2 |