View source for Psilomelane

{{Short description|Hard black manganese oxides (romanechite, mainly)}}
{{No footnotes|date=February 2023}}
{{Infobox mineral
| name        = Psilomelane
| category    = [[Oxide minerals]]
| boxwidth    = 
| boxbgcolor  = 
| image       = Mineraly.sk - psilomelan.jpg
| imagesize   = 260px
| caption     = 
| formula     = General formula:<br>{{chem2|Ba(Mn(2+))(Mn(4+))8O16(OH)4}}, or as {{chem2|(Ba,H2O)2Mn5O10}}<br>Barium manganese oxide hydroxide
| molweight   = 590.03 g/mol
| system      = [[Monoclinic]]
| color       = Black with gray [[pyrolusite]] bands
| habit       = [[Botryoidal]], [[mammillary]], [[Crystal habit#List of crystal habits|reniform]]
| twinning    = 
| cleavage    = None
| fracture    = [[Conchoidal]] and uneven
| mohs        = 5.0 – 6.0
| luster      = Sub-metallic, dull
| polish      = Vitreous to [[Lustre (mineralogy)#Adamantine lustre|subadamantine]]
| refractive  = 
| opticalprop = 
| birefringence = 
| pleochroism = 
| streak      = Brownish black
| gravity     = 3.7 – 4.7
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = in [[hydrochloric acid]]
| diaphaneity = Opaque
| other       = Hard black [[manganese oxide]]s such as [[hollandite]] and [[romanechite]] 
}}

'''Psilomelane''' is a group name for hard black [[manganese oxide]]s including [[hollandite]] and [[romanechite]]. Psilomelane consists of hydrous [[manganese]] oxide with variable amounts of [[barium]] and [[potassium]]. Psilomelane is erroneously, and uncommonly, known as '''black hematite''', despite not being related to true [[hematite]], which is an iron oxide.

==Formula==
Generalized formula may be represented as {{chem2|Ba(Mn(2+))(Mn(4+))8O16(OH)4}} or as {{chem2|(Ba,H2O)2Mn5O10}}. It is sometimes considered to be a hydrous manganese [[manganate]], but of doubtful composition. The amount of manganese present corresponds to 70-80% of [[Manganese(II) oxide|manganous oxide]] with 10-15% of available [[oxygen]]. 

==Characteristics==
Psilomelane has no definite [[chemical composition]] and occurs as [[botryoidal]] and [[Speleothem|stalactitic]] masses with a smooth shining surface and submetallic lustre.  The [[mineral]] is readily distinguished from other hydrous manganese oxides ([[manganite]] and [[Wad (mineral)|wad]]) by its greater [[Mohs scale of mineral hardness|hardness]] 5 to 6; the [[specific gravity]] 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 hydroxide]]s. It is soluble in [[hydrochloric acid]] with evolution of [[chlorine]] gas.

==History and occurrence==
The name, dating back to 1758, makes reference to its characteristic appearance, from the [[Greek language|ancient Greek]] ''ψιλός: psilos'' for (naked, smooth, bald) and ''μέλας: melas'' (black); a [[Latin]]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]] in [[Cornwall]], [[Brendon Hills]] in [[Somerset]], [[Hoy, Orkney|Hoy]] in [[Orkney]], Sayn near [[Coblenz]], Hout Bay near [[Cape Town]], and Crimora in Augusta county, Virginia. With pyrolusite it is extensively mined in [[Vermont]], [[Virginia]], [[Arkansas]], and [[Nova Scotia]].

==Image gallery==
<gallery widths="150px" heights="120px">
File:Psilomelane-167850.jpg|A specimen of [[manganese oxide]] 
File:Psilomelane-dendrites.jpg|[[Dendrite (crystal)|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]], Germany
File:Vanadinite-Psilomelane-112809.jpg|[[Vanadinite]] and psilomelane from Taouz, Er Rachidia Province, Meknès-Tafilalet Region, Morocco
</gallery>

==See also==
{{Commons category|Psilomelane}}
{{Wikt|psilomelane}}
Other manganese oxides: 
* [[Birnessite]]
* [[Hollandite]]
* [[Pyrolusite]]
* [[Romanechite]]

==References==
* {{1911|wstitle=Psilomelane|volume=22|page=542}}
* [http://www.mindat.org/show.php?id=3304&ld=1&pho= Mindat with locality data]
* [http://webmineral.com/data/Psilomelane.shtml Webmineral]
* [https://web.archive.org/web/20051121001756/http://mineral.galleries.com/minerals/oxides/psilomel/psilomel.htm Mineral galleries]

{{Manganese minerals}}

[[Category:Barium minerals]]
[[Category:Manganese(II,IV) minerals]]
[[Category:Oxide minerals]]
[[Category:Monoclinic minerals]]