File:Snowflake obsidian 22.jpg
![File:Snowflake obsidian 22.jpg](https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Snowflake_obsidian_22.jpg/800px-Snowflake_obsidian_22.jpg?20230420151916)
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Summary
[edit]DescriptionSnowflake obsidian 22.jpg |
English: (field of view ~7.4 centimeters across)
Igneous rocks form by the cooling and crystallization of hot, molten rock (magma and 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. Obsidian is readily identifiable. It is a glassy-textured, extrusive igneous rock. Obsidian is natural glass - it lacks crystals, and therefore lacks minerals. Obsidian is typically black in color, but most obsidians have a felsic to intermediate chemistry. Felsic igneous rocks are generally light-colored, so a felsic obsidian seems a paradox. Mafic obsidians are scarce, but they are also black and glassy. Obsidian is sometimes referred to "glassy rhyolite". Obsidian is an uncommon rock, but can be examined at several famous localities in America, such as Obsidian Cliff at the Yellowstone Hotspot (northwestern Wyoming, USA) and Big Obsidian Flow at the Newberry Volcano (central Oregon, USA). Obsidian is moderately hard and has a conchoidal fracture (smooth and curved fracture surface), with sharp broken edges. Freshly-broken obsidian has the sharpest edges of any material known, natural or man-made (as seen under a scanning electron microscope). Obsidian forms two ways: 1) very rapid cooling of lava, which prevents the formation of crystals; 2) cooling of high-viscosity lava, which prevents easy movement of atoms to form crystals. An example of obsidian that formed the first way is along the margins of basaltic lava flows at Kilaeua Volcano (Hawaii Hotspot, central Pacific Ocean). The obsidian sample seen here formed the second way. Obsidian is unstable on geologic time scales - it will slowly convert to material that is not obsidian. A partially-converted obsidian is a distinctive rock called snowflake obsidian. The black portions of the rock seen here are rhyolitic obsidian (glass). The white patches ("snowflakes") are devitrification spots composed of cristobalite (SiO2, a polymorph of quartz). Locality: unrecorded / undisclosed, but possibly from Twin Peaks, Utah, USA |
Date | |
Source | https://www.flickr.com/photos/47445767@N05/52825267887/ |
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@N05/52825267887. It was reviewed on 20 April 2023 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
20 April 2023
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current | 15:19, 20 April 2023 | ![]() | 3,843 × 2,522 (5.99 MB) | Ser Amantio di Nicolao (talk | contribs) | Uploaded a work by James St. John from https://www.flickr.com/photos/47445767@N05/52825267887/ with UploadWizard |
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot D10 |
Exposure time | 1/60 sec (0.016666666666667) |
F-number | f/10 |
ISO speed rating | 80 |
Date and time of data generation | 12:35, 17 April 2023 |
Lens focal length | 9.681 mm |
Width | 4,000 px |
Height | 3,000 px |
Bits per component |
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Pixel composition | RGB |
Orientation | Normal |
Number of components | 3 |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop Elements 18.0 (Macintosh) |
File change date and time | 19:49, 17 April 2023 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 12:35, 17 April 2023 |
Meaning of each component |
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Image compression mode | 3 |
APEX shutter speed | 5.90625 |
APEX aperture | 6.65625 |
APEX exposure bias | −0.33333333333333 |
Maximum land aperture | 3.625 APEX (f/3.51) |
Metering mode | Pattern |
Flash | Flash fired, compulsory flash firing, red-eye reduction mode |
Supported Flashpix version | 1 |
Color space | sRGB |
Focal plane X resolution | 16,460.905349794 |
Focal plane Y resolution | 16,483.516483516 |
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 |
Lens used | 6.2-18.6 mm |
Date metadata was last modified | 15:49, 17 April 2023 |
Unique ID of original document | 94714828BD2835EF376CB2B9C004AA2E |