MARTIN LAND / SCIENCE PHOTO LIBRARY MARTIN LAND / SCIENCE PHOTO LIBRARY
Perthite. This is a striped variety of a feldspar mineral. Feldspars contain silicates of aluminium together with varying amounts of potassium, calcium or sodium. Here the blue layers are microcline, a potassium feldspar (formula: KAlSi3O8). The white layers formed due to changes in temperature during mineral formation. This altered the feldspar chemistry, colour and crystal structure. Feldspars are the most common minerals in the Earth's crust, found in igneous and metamorphic rocks. They decompose to form a major constituent of clay soils. Microcline is used in the manufacture of porcelain and glass. This specimen is from the Rio Grande, Brazil.
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