Paul English, age 13, of Galveston, Tex., for his question:
WHAT IS GEOCHEMISTRY?
Geochemistry is the chemistry of the Earth. A geochemist makes chemical analyses of the composition of minerals and rocks and from these he learns what changes took place in the formation of minerals. He also learns how the chemical elements are distributed in the rocks.
Geochemistry is somewhat new as a science. Although some geochemical studies were made as far back as 1840, most of the important work has been done since 1900.
In 1908 a chemist named Frank Clarke published the first important book containing chemical analyses of more than 5,000 rocks, minerals, sediments and waters. The book was put out by the United States Geological Survey.
It was with this report that we learned that of the 90 naturally occurring chemical elements, 12 make up more than 99 percent of the outer crust on which we live.
Probably the most important person in the field of geochemistry was the Norwegian geochemist named Victor Goldschmidt. His work went beyond making chemical analyses of minerals and rocks. He was interested in learning why certain chemical elements are always found as impurities in certain minerals.
Goldschmidt recognized that atoms of different elements have different sizes. He also knew that the valence, or combining power, of atoms of different elements varied. These two things helped to explain the presence of impurities.
The knowledge that certain chemical elements are found in rocks and minerals helps to locate metal ores. It is known, for example, that a rock exposed to rain, wind, ice, heat and cold breaks up slowly. The minerals crumble away and dissolve and some of the elements in them go into the soil that covers the bedrock.
Plants living on this soil absorb some of these elements into their roots and leaves. The geochemist analyzes samples of soil and plants to determine the elements in them. In this way he can learn something about the bedrock that lies underneath.
Geochemistry also covers the chemical composition of mud and sand sediments that form on beaches and sea bottoms today. These materials will be compacted into sedimentary rocks many thousands of years from now.
Their chemical compositions are analyzed and compared with the compositions of rocks that were mud and sand long ago. These geochemical studies tell what chemical changes take place when sedimentary rocks are formed.
The geochemist also makes chemical analyses of water from oceans, rivers, lakes, swamps, wells and hot springs. All these natural waters contain dissolved compounds such as salt. The ocean is about three percent dissolved solids. Most rivers and lakes have much less than one percent.
As a result of years of studies, the geochemical cycle has become known. This cycle is made up of the processes through which chemical elements pass in the many stages of rock and mineral development.