Jasper is an opaque form of chalcedony, which is a microcrystalline variety of the mineral quartz. It is typically red, brown, yellow, or green in colour, but it can also be found in other colours, such as black, white, and blue. Jasper is formed when silica-rich fluids precipitate from hot springs or hydrothermal vents. The colour of jasper is determined by the impurities that are present in the silica-rich fluids. For example, red jasper is typically caused by the presence of iron oxide, while green jasper is typically caused by the presence of chlorite.
Jasper is a relatively common gemstone and can be found in many parts of the world, including Australia, Brazil, India, and the United States.