Turquoise is a hydrated phosphate mineral composed of copper, aluminum, and iron, with the chemical formula CuAl₆(PO₄)₄(OH)₈·4H₂O. It is most known for its vibrant blue to green color, which is influenced by the presence of copper for blue hues and iron for green tones. Turquoise has a Mohs hardness of 5 to 6, making it relatively soft and prone to scratching, so it is often used in jewelry with proper care. It forms in arid, copper-rich environments, often found in limestone or sandstone deposits. Major sources include the United States, Iran, China, and Egypt.