Jasper

A variety of Chalcedony

In the traditional sense, jasper is a dense, opaque, microcrystalline variety of quartz (or more strictly, chalcedony), usually red, brown or yellow and coloured by oxides of iron. It has frequently been used as a decorative stone.

Confusingly the term is also used for other silicified rocks or decorative stones (in particular some varieties of rhyolite are often termed jasper).