gems, quartz, cryptocrystalline quartz, chalcedony, agate, jasper, jasperoid

A review of the genetic classifications of jasper based on mineralogical data outlines three main types of jasper and related rocks: 1 – jaspers; 2 – jasperoids; 3 – jasper-like rocks. True jasper has a quartz composition and is of metamorphic or metasomatic origin. Related in different colour and density to jasper, other rocks of sedimentary or igneous origin can be found, usually having a dominantly chalcedony–quartz and feldspar–quartz composition (jasperoids and jasper-like rocks). Main mineral impurities which cause the colour of the described rocks are listed.