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Soil Formation

In the end, Earth rocks which started life as granite and related igneous rocks, become a soil. This soil consists of coarse quartz-sand particles, intermediate sized silt particles, and fine silicate clays. Soil also contains the residue of salts such as carbonates, nitrates and other contaminants which dissolve in groundwater. Some of the sand, silt, and clay and most of the dissolved materials are carried out to sea as part of the water cycle. That which remains as soil is virtually resistant to further chemical decomposition. The picture to the left summarizes the process. Rocks break apart as part of the weathering process (sometimes helped by tree roots) into the smallest parts, and these parts supply nutrients for plants.

Almost all of the soil-derived nutrients required by plants, animals, and human beings are found in the minerals in granite and other igneous rocks. Among the others are apatite, a carrier of phosphorus; pyrite, a compound of iron and sulfer, purolusite, a source of manganeses; and tourmaline, the source of most of the boron in soils and in plants growing in them.

Much of these mineral nutrients dissolve out of rock during the soil-forming process and are lost to sea. But enough attaches to fine clay particles to meet the needs of plants that ultimately come into being. As these plants die, and fall back onto the ground, they return the mineral elements to the land from which they had come. This returned portion is in a more readily usable state for new growths of plants than that that which was originally contained in clay.


This picture shows the sediments from which soil is formed.
Click on image for full size version (40K GIF)

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Soil Formation

In the end, Earth rocks which started life as granite and related igneous rocks, become a soil. This soil consists of big sand particles, medium sized silt particles, and small clay particles. Soil also contains nutrients such as carbonates, and nitrates which dissolve in groundwater.

Some of the sand, silt, and clay and most of the dissolved materials are carried out to sea as part of the water cycle. That which remains as soil and can't be dissolved any further. The picture to the left summarizes the process. Rocks break apart as part of the weathering process (sometimes helped by tree roots) into the smallest parts, and these parts supply nutrients for plants.

All of the soil-derived nutrients required by plants, animals, and human beings are found in the minerals in granite and other igneous rocks. Much of these mineral nutrients dissolve out of rock during the soil-forming process and are lost to sea. But enough attaches to fine clay particles to meet the needs of plants. As these plants die, and fall back onto the ground, they return the mineral elements to the land from which they had come.


This picture shows the sediments from which soil is formed.
Click on image for full size version (40K GIF)

Return to Geology

Go to a listing of Rocks


Soil Formation

In the end, Earth rocks which started life as granite and related igneous rocks, become soil as part of the weathering process. This soil consists of big sand particles, medium sized silt particles, and small clay particles. Soil also contains nutrients which dissolve in groundwater. As shown in the picture to the left, rocks break apart (sometimes helped by tree roots) into the smallest parts, and these parts supply nutrients for plants.

Some of the sand, silt, and clay and most of the dissolved materials are carried out to sea as part of the water cycle. That which remains is soil.

Minerals in granite and other igneous rocks supply all of the nutrients required by plants, animals, and human beings. As these plants die, and fall back onto the ground, they return the mineral elements to the land from which they had come.


This picture shows the sediments from which soil is formed.
Click on image for full size version (40K GIF)

Return to Geology

Go to a listing of Rocks



Last modified February 15, 1998 by the Windows Team

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