File:Skeletal quartz (Zhob District, Pakistan) 1 (34479432632).jpg

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Smoky quartz from Pakistan.

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 5100 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.

The simplest & most abundant silicate mineral in the Earth's crust is quartz (SiO2). All other silicates have silica + impurities. Many silicates have a significant percentage of aluminum (the aluminosilicates).

Quartz (silicon dioxide/silica - SiO2) is the most common mineral in the Earth's crust. It is composed of the two most abundant elements in the crust - oxygen and silicon. It has a glassy, nonmetallic luster, is commonly clearish to whitish to grayish in color, has a white streak, is quite hard (H≡7), forms hexagonal crystals, has no cleavage, and has conchoidal fracture. Quartz can be any color: clear, white, gray, black, brown, pink, red, purple, blue, green, orange, etc.

Smoky quartz is gray or brown or black-colored. The dark coloration is due to natural radiation bombardment. Dark-colored quartz can also be due to inclusions.

Locality: unrecorded/undisclosed site in Zhob District, northwestern Pakistan


Photo gallery of quartz and smoky quartz: <a href="http://www.mindat.org/gallery.php?min=3337" rel="nofollow">www.mindat.org/gallery.php?min=3337</a> and

<a href="https://www.mindat.org/gallery.php?min=3689" rel="nofollow">www.mindat.org/gallery.php?min=3689</a>
Date
Source Skeletal quartz (Zhob District, Pakistan) 1
Author James St. John

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This file is licensed under the Creative Commons Attribution 2.0 Generic license.
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/34479432632 (archive). It was reviewed on 5 December 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

5 December 2019

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Date/TimeThumbnailDimensionsUserComment
current02:06, 5 December 2019Thumbnail for version as of 02:06, 5 December 20191,875 × 2,183 (2.74 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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