File:Tourmaline in pegmatitic granite 1 (26934247769).jpg
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[edit]DescriptionTourmaline in pegmatitic granite 1 (26934247769).jpg |
Tourmaline in pegmatitic granite Black = schorl tourmaline Light, cream-colored = potassium feldspar Glassy gray = quartz A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 5400 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates. The silicates are the most abundant and chemically complex group of minerals. All silicates have silica as the basis for their chemistry. "Silica" refers to SiO2 chemistry. The fundamental molecular unit of silica is one small silicon atom surrounded by four large oxygen atoms in the shape of a triangular pyramid - this is the silica tetrahedron - SiO4. Each oxygen atom is shared by two silicon atoms, so only half of the four oxygens "belong" to each silicon. The resulting formula for silica is thus SiO2, not SiO4. Tourmaline is a classic "garbage-can mineral" - it has a little bit of just about everything. Tourmaline can be given the formula (Na,Ca)(Li,Mg,Al)(Fe,Mn,Al)6(BO3)3(Si6O18)(OH,F)4 - sodium calcium lithium magnesium iron manganese hydroxy-fluoro-boro-aluminosilicate. Tourmaline has a nonmetallic luster, varies in color but is often blackish, has a white streak, is quite hard (H = 7 to 7.5), frequently has elongated crystals with subtriangular cross-sections and striated faces, no cleavage, and conchoidal fracture. Tourmaline is a group of minerals, the most common of which is the blackish-colored, Fe-rich schorl. Other varieties include achroite, dravite (= Mg-rich), elbaite (= Li & Na-rich), indicolite, liddicoatite (= Li & Ca-rich), rubellite, verdelite, and others. The latter-listed tourmalines are often richly colored (greenish, yellowish, reddish, pinkish, bluish, multicolored). Tourmaline is moderately common in pegmatites and some metamorphic rocks. It can even be rock-forming - see the scarce rock tourmalinite (<a href="https://www.flickr.com/photos/jsjgeology/15095512541">www.flickr.com/photos/jsjgeology/15095512541</a>). The black-colored areas are clusters of small tourmaline sticks (click on the photo to zoom in and look around). The host rock is pegmatite, or pegmatitic granite. Pegmatites are very coarsely-crystalline textured, intrusive igneous rocks. Their large crystal size is the result of cooling of water-rich magmas. Pegmatites often have concentrations of unusual elements, which is conducive to the formation of less common minerals such as uraninite, beryl, and tourmaline. Photo gallery of tourmaline: <a href="http://www.mindat.org/gallery.php?min=4003" rel="nofollow">www.mindat.org/gallery.php?min=4003</a> |
Date | |
Source | Tourmaline in pegmatitic granite 1 |
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@N05/26934247769 (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 | 04:16, 12 November 2019 | ![]() | 4,000 × 2,528 (5.02 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 | 1/60 sec (0.016666666666667) |
F-number | f/9 |
ISO speed rating | 80 |
Date and time of data generation | 15:07, 17 November 2017 |
Lens focal length | 8.295 mm |
Image title | |
Width | 4,000 px |
Height | 3,000 px |
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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 13.0 (Macintosh) |
File change date and time | 12:08, 28 November 2017 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 15:07, 17 November 2017 |
Meaning of each component |
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APEX shutter speed | 5.90625 |
APEX aperture | 6.34375 |
APEX exposure bias | −0.66666666666667 |
Maximum land aperture | 3.34375 APEX (f/3.19) |
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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 | Portrait |
Lens used | 6.2-18.6 mm |
Date metadata was last modified | 07:08, 28 November 2017 |
Unique ID of original document | 58EB1245A2D1BE140E83C539DBFE0C1A |
IIM version | 29,735 |