Psilomelane is a group name for hard black manganese oxides including hollandite and romanechite. Psilomelane consists of hydrous

manganese Manganese is a chemical element; it has Symbol (chemistry), symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese was first isolated in the 1770s. It is a transition m ...

oxide with variable amounts of barium and

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

. Psilomelane is erroneously, and uncommonly, known as black hematite, despite not being related to true

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

, which is an iron oxide.

Formula

Generalized formula may be represented as or as . 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 Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

Characteristics

Psilomelane has no definite chemical composition and occurs as botryoidal and stalactitic masses with a smooth shining surface and submetallic lustre. The

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2011): Mi ...

is readily distinguished from other hydrous manganese oxides ( manganite and wad) by its greater

hardness In materials science, hardness (antonym: softness) is a measure of the resistance to plastic deformation, such as an indentation (over an area) or a scratch (linear), induced mechanically either by Pressing (metalworking), pressing or abrasion ...

5 to 6; the

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

varies from 3.7 to 4.7. The streak is brownish black and the fracture smooth. The mineral often contains admixed impurities, such as iron hydroxides. It is soluble in hydrochloric acid with evolution of

chlorine Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

gas.

History and occurrence

The name, dating back to 1758, makes reference to its characteristic appearance, from the

ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

''ψιλός: psilos'' for (naked, smooth, bald) and ''μέλας: melas'' (black); a

Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...

ized form is calvonigrite from ''calvo'' for (bald, smooth) and ''negri'' (black). It is a common and important ore of manganese, occurring under the same conditions and having the same commercial applications as pyrolusite. It is found at many localities; amongst those which have yielded typical botryoidal specimens may be mentioned the Restormel iron mine at

Lostwithiel Lostwithiel (; ) is a civil parish and small town in Cornwall, England, United Kingdom at the head of the estuary of the River Fowey. According to the 2001 census it had a population of 2,739, increasing to 2,899 at the 2011 census. The Lostwi ...

Cornwall Cornwall (; or ) is a Ceremonial counties of England, ceremonial county in South West England. It is also one of the Celtic nations and the homeland of the Cornish people. The county is bordered by the Atlantic Ocean to the north and west, ...

, Brendon Hills in

Somerset Somerset ( , ), Archaism, archaically Somersetshire ( , , ) is a Ceremonial counties of England, ceremonial county in South West England. It is bordered by the Bristol Channel, Gloucestershire, and Bristol to the north, Wiltshire to the east ...

, Hoy in

Orkney Orkney (), also known as the Orkney Islands, is an archipelago off the north coast of mainland Scotland. The plural name the Orkneys is also sometimes used, but locals now consider it outdated. Part of the Northern Isles along with Shetland, ...

, Sayn near Coblenz, Hout Bay near

Cape Town Cape Town is the legislature, legislative capital city, capital of South Africa. It is the country's oldest city and the seat of the Parliament of South Africa. Cape Town is the country's List of municipalities in South Africa, second-largest ...

, and Crimora in Augusta county, Virginia. With pyrolusite it is extensively mined in

Vermont Vermont () is a U.S. state, state in the New England region of the Northeastern United States. It borders Massachusetts to the south, New Hampshire to the east, New York (state), New York to the west, and the Provinces and territories of Ca ...

Virginia Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...

Arkansas Arkansas ( ) is a landlocked state in the West South Central region of the Southern United States. It borders Missouri to the north, Tennessee and Mississippi to the east, Louisiana to the south, Texas to the southwest, and Oklahoma ...

, and

Nova Scotia Nova Scotia is a Provinces and territories of Canada, province of Canada, located on its east coast. It is one of the three Maritime Canada, Maritime provinces and Population of Canada by province and territory, most populous province in Atlan ...

Image gallery

File:Psilomelane-167850.jpg, A specimen of manganese oxide File:Psilomelane-dendrites.jpg, Dendritic psilomelane on a cobble File:Psilomelane+Hausmanite.jpg, Slab of manganese ore showing a mixture of hausmannite and psilomelane in a zonal arrangement and a radiating mass of white barite at the center File:Psilomelane-pyrolusite 7100.4947.jpg, Psilomelane and pyrolusite from Solnhofen Limestone quarries, Solnhofen, Franconia,

Bavaria Bavaria, officially the Free State of Bavaria, is a States of Germany, state in the southeast of Germany. With an area of , it is the list of German states by area, largest German state by land area, comprising approximately 1/5 of the total l ...

, Germany File:Vanadinite-Psilomelane-112809.jpg, Vanadinite and psilomelane from Taouz, Er Rachidia Province, Meknès-Tafilalet Region, Morocco

References

*
Mindat with locality data

Webmineral

{{Manganese minerals Barium minerals Manganese(II,IV) minerals Oxide minerals Monoclinic minerals

Formula

Characteristics

History and occurrence

Image gallery

See also

References