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TITLE: Building Blocks of Rocks

[Photo: Pie Chart]

Silicates make up the majority of rocks in our planet's crust and upper mantle. This chart shows the relative abundance of minerals in the Earth's crust. A total of 89 percent are silicates. Each major silicate family is defined by a characteristic arrangement of silicon and oxygen atoms.

The feldspar mineral family composes about half of the Earth's crust. All the feldspars have the same three-dimensional framework of silicon (Si), oxygen (O), and aluminum (Al) atoms. The most common feldspar minerals also contain potassium (K), sodium (Na), or calcium (Ca). See feldspar specimens in the GeoGallery.


In the layer silicates, silicon (Si) and oxygen (O) atoms connect to form sheets, with other atoms sandwiched in-between. Layer silicates are the major constituent of most clays and muds. See layer silicates in the GeoGallery.

See caption at left.


In the pyroxenes, silicon (Si) and oxygen (O) atoms connect in long chains that are interlinked by other kinds of atoms. They are commonly found in dark-colored volcanic rocks and are a major component of the Earth's mantle. See pyroxenes in the GeoGallery.

See caption at left.


In the amphiboles, silicon (Si) and oxygen (O) atoms connect in double chains. Amphiboles contain water, so they are usually found in rocks that formed under water-rich conditions. See amphiboles in the GeoGallery.

See caption at left.


Quartz is a major constituent of beach sand and an important component of many types of rocks. Quartz is composed of the elements silicon and oxygen forming a hexagonal shaped pattern. See Quartz in the GeoGallery.


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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits