Jasper is a microcrystalline variety of Quartz, a silicon dioxide mineral with a hardness of 6.5 to 7. Its crystal system is hexagonal (trigonal). In Jasper, the Quartz microcrystals are laid out in sugar-like grains, rather than the fibrous layers found in its close relative, Chalcedony. The name Jasper is derived from a Greek word meaning ‘spotted stone.’ Jaspers can include up to 20% foreign materials, which account for its wide variety of colors and patterns. It occurs in nodules or as fillings in fissures. Jaspers are found all over the world.
Simmons, Robert; Ahsian, Naisha. The Book of Stones, Revised Edition: Who They Are and What They Teach (several pages). North Atlantic Books. Kindle Edition.