As a pure natural stone, pebbles are formed by broken rock blocks that disappear after a long time of water brushing and form round or elliptical stones (or pebbles and gravels). The main component is SiO2 followed by a small amount of iron oxide and a trace amount of elements such as sulphur, copper, aluminum, magnesium and the like. Since the types and contents of these pigment particles dissolved in the SiO2 hydrothermal fluid are unfair, they exhibit a color that varies in shades and shades, and the cobblestones are colored in black, white, yellow, red, dark green, and grayish gray.