Feldspathoid

Minerals occurring in low-Si terrestrial rocks, feldspathoids are similar to feldspars in structure and properties, but contain about two-thirds as much silicaSilicon dioxide, SiO2. as alkali feldsparVariety of feldspar containing alkali metals potassium and sodium in a solid solution. A more complete explanation can be found on the feldspar group page that also includes the plagioclase feldspars as part of the feldspar ternary diagram. Click on Term to Read More. They do not coexist with quartzComposed of SiO2, quartz is one of the silica group minerals most common in Earth's crust, but never found in meteorites as inclusions visible to the naked eye. Quartz in meteorites has been found in very small quantities in eucrites, other calcium-rich achondrites, and in the highly reduced E chondrites. Click on Term to Read More, because the excess of SiO₂ converts feldspathoids into feldsparAn alumino-silicate mineral containing a solid solution of calcium, sodium and potassium. Over half the Earth’s crust is composed of feldspars and due to their abundance, feldspars are used in the classification of igneous rocks. A more complete explanation can be found on the feldspar group page. Click on Term to Read More. The most common feldspathoids are: nepheline, NaAlSiO₄, falsilite, KAlSiO₄, and leucite, KAlSi₂O₆. Their compositions can be displayed using a tetrahedron with quartz at the apex (below). The ranges of observed substitutions are shown by the colored fields.