Periclase
Periclase occurs naturally in contact metamorphic rocks and is a major component of most basic refractory bricks. It is a cubic form of magnesium oxide. It was first described in 1840 and named from the Greek περικλάω in allusion to its cleavage. The type locality is Monte Somma, Somma-Vesuvius Complex, Naples Province, Campania, Italy. The old term for the mineral is
magnesia. Stones from the Magnesia region in ancient Anatolia contained both magnesium oxide and hydrated magnesium carbonate as well as iron oxides. Thus these stones, called
Stones from Magnesia in antiquity, with their unusual
magnetic properties were the reason the terms
magnet and
magnetism were coined. Periclase is usually found in marble produced by metamorphism of dolomitic limestones. It readily alters to brucite under near surface conditions. In addition to its type locality, it is reported from Predazzo, Tyrol, Austria; Carlingford, County Louth, Ireland; Broadford, Skye and the island of Muck, Scotland; León, Spain; the Bellerberg volcano, Eifel district, Germany; Nordmark and Långban, Varmland, Sweden; and Kopeysk, southern Ural Mountains, Russia.