The mineral part of soil forms from rocks. Such forces as wind, water, and temperature changes break rocks down into tiny particles, or bits. The smallest particles are called clay. Medium-sized particles are called silt. The largest particles are called sand. Different types of soil contain different mixtures of clay, silt, and sand.
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How soils formThe organic part of soil forms when plants and animals die. Their bodies decay, or break down, and mix with the rock particles. The organic material, called humus, helps to form the pores in the soil. It keeps the soil soft and loose. Humus also provides the nutrients used by plants.
