What is "jasperoid"

a. Resembling jasper. n. (context mineralogy English) A rare dense siliceous rock similar in appearance to chert.

Jasperoid is a rare, peculiar type of metasomatic alteration and occurs in two main forms; sulfidic jasperoids and hematitic jasperoids. True jasperoids are different from jaspillite, which is a form of metamorphosed chemical sedimentary rock, and from jasper which is a chemical sediment.

Sulfidic jasperoids are typical examples of silica- sulfide metasomatism of dolostones, and are found in Nevada and Iran. They are hard, dense purple-black rocks with considerable content of pyrite. The bodies in Nevada are quite thin (seldom greater than 8 m) and stratabound.