Mud is a mixture of water and soil. Soil is composed of minerals, organic matter, and water. The most common minerals in soil are sand, silt, and clay. Sand is the largest of the three particles and is composed of quartz, a hard mineral. Silt is smaller than sand and is composed of various minerals, including quartz, feldspar, and mica. Clay is the smallest of the three particles and is composed of clay minerals, which are very tiny and have a plate-like shape. Organic matter in soil comes from plants and animals that have died and decomposed. Water is essential for plant growth and is also important for the chemical and biological processes that occur in soil.