1911 Encyclopædia Britannica/Psilomelane

PSILOMELANE, a mineral consisting of hydrous manganese oxide with variable amounts of barium, potassium, &c. It is sometimes considered to be a hydrous manganese manganate, but of doubtful composition. The amount of manganese present corresponds to 70–80% of manganous oxide with 10–15% of “available” oxygen. The mineral is amorphous and occurs as botryoidal and stalactitic masses with a smooth shining surface and submetallic lustre. The name has reference to this characteristic appearance, being from the Greek ψιλός (naked, smooth) and μέλας (black); a Latinized form is calvonigrite, and a German name with the same meaning is Schwarzer Glaskopf. Psilomelane is readily distinguished from other hydrous manganese oxides (manganite and wad) by its greater hardness (H. = 51/2); the sp. gr. varies from 3·7 to 4·7. The streak is brownish-black and the fracture smooth. Owing to its amorphous nature, the mineral often contains admixed impurities, such as iron hydrates. It is soluble in hydrochloric acid with evolution of chlorine. It is a common and important ore of manganese, occurring under the same conditions and having the same commercial applications as pyrolusite (q.v.). It is found at many localities; amongst those which have yielded typical botryoidal specimens may be mentioned the Restormel iron mine at Lostwithiel in Cornwall, Brendon Hill in Somerset, Hoy in the Orkneys, Sayn near Coblenz, and Crimora in Augusta county, Virginia. With pyrolusite it is extensively mined in Vermont, Virginia, Arkansas and Nova Scotia.