Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula SiO2. It is a natural compound made of two of the earths most abundant materials: silicon and oxygen. Silicon dioxide is commonly found in nature as quartz and is the major constituent of sand in many parts of the world. It is also abundant in the earths crust, making up more than 95% of known rocks on the planet. Silicon dioxide is mostly obtained by mining, including sand mining and purification of quartz. Quartz is suitable for many purposes, while chemical processing is required to make a purer or otherwise more suitable product. Silicon dioxide is found naturally in many foods and beverages, such as leafy green vegetables, beets, bell peppers, brown rice, oats, alfalfa, bananas, eggs, fish, grains, green beans, milk, and water. It is also added to many foods and supplements as an anticaking agent to avoid clumping. Numerous studies suggest that there is no cause for concern when people consume silicon dioxide in normal doses, such as the small amounts added to foods.