Sulphur is a chemical element with an atomic number of 16 and an atomic symbol of S. At room temperature it is a yellow crystalline solid. Even though it is insoluble in water, it is one of the most versatile elements at forming compounds. Sulphur reacts and forms compounds with all elements except gold, iodine, iridium, nitrogen, platinum, tellurium, and the inert gases. Sulphur is abundant and occurs throughout the Universe, but it is rarely found in a pure, uncombined form at Earth's surface. As an element, sulphur is an important constituent of sulphate and sulphide minerals. It occurs in the dissolved ions of many waters. It is an important constituent of many atmospheric, subsurface, and dissolved gases. It is an essential element in all living things and is in the organic molecules of all fossil fuels - "".