Occurrence and Origin of Minerals

Abstract

Through deep core drilling or mountain building processes coupled with erosion, the chemistry and distribution of elements in rocks is known to us as far into the earth as the top of the subcrustal layer, marked by the Mohorovičić discontinuity, or at least to a depth of about 16 km. In 1924 Clarke and Washington, after studying some 5000 rock analyses, were able to describe the relative abundance of the most important elements in the earth’s crust. They discovered that only a small portion of the 92 elements found in crustal rocks are important constituents. Nearly 99.5%, by weight, of the earth’s crust is made up of only 12 elements, of which two, oxygen and silicon, comprise 75% of the total weight. Expressed in percent by volume, the oxygen content alone is over 94%. Consequently, the most important minerals in the crust are the oxygen-silicon compounds, the silicates.