Psilomelane
617607
211914631
2008-05-12T17:50:06Z
Tillman
1663062
add photo, remove another (Mn metal), copyedit
{{Infobox mineral
| name = Psilomelane
| category =
| boxwidth =
| boxbgcolor =
| image = Mineraly.sk - psilomelan.jpg
| caption = A native sample of psilomelane
| formula = The general formula<br>Ba(Mn<sup>2+</sup>)(Mn<sup>4+</sup>)<sub>8</sub>O<sub>16</sub>(OH)<sub>4</sub> or as (Ba,H<sub>2</sub>O)<sub>2</sub>Mn<sub>5</sub>O<sub>10</sub><br>Barium Manganese Oxide Hydroxide
| molweight = 590.03 gm
| color = black with gray pyrolusite bands
| habit = Botryoidal, Mammillary, Reniform
| system = monoclinic
| twinning =
| cleavage = none
| fracture = conchoidal and uneven
| mohs = 5.0 - 6.0
| luster = Sub-Metallic, Dull
| polish = vitreous to 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]]
| var1 =
| var2 =
| var3 =
| var4 =
| var5 =
| var6 =
}}
[[Image:Psilomelane+Hausmanite.jpg|thumb|tight|Polished specimen of manganese ore from the [[Batesville, Arkansas]] district. Slab of manganese ore showing an intimate mixture of [[hausmannite]] and psilomelane in a roughly zonal arrangement and a radiating mass of white [[barite]] at the center. The light steel-gray mineral and the black mineral immediately adjacent to the barite are '''psilomelane'''. The rest of the black mineral is '''hausmannite.''' Natural size.]]
'''Psilomelane''', also known as '''black hematite''', is a group name for hard black [[manganese oxide]]s such as hollandite and [[romanechite]]. Psilomelane consists of hydrous [[manganese]] oxide with variable amounts of [[barium]] and [[potassium]].
==Formula==
Generalized formula may be represented as Ba(Mn<sup>2+</sup>)(Mn<sup>4+</sup>)<sub>8</sub>O<sub>16</sub>(OH)<sub>4</sub> or as (Ba,H<sub>2</sub>O)<sub>2</sub>Mn<sub>5</sub>O<sub>10</sub>. 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]].
==Characteristics==
Psilomelane is amorphous and occurs as botryoidal and stalactitic masses with a smooth shining surface and submetallic lustre. The [[mineral]] is readily distinguished from other hydrous manganese oxides (manganite and 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. Owing to its [[amorphous]] nature, 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 has reference to this characteristic appearance, from the [[Greek language|Greek]] for (naked, smooth) and (black); a [[Latin]]ized form is calvonigrite, and a [[German language|German]] name with the same meaning is '''Schwarzer Glaskopf'''.
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]] in [[Orkney]], Sayn near [[Coblenz]], and Crimora in Augusta county, Virginia. With pyrolusite it is extensively mined in [[Vermont]], [[Virginia]], [[Arkansas]], and [[Nova Scotia]].
Psilomelane is also cut, shaped, and polished for a variety of jewelry applications.
==References==
*{{1911}}
* [http://www.mindat.org/show.php?id=3304&ld=1&pho= Mindat with locality data]
* [http://webmineral.com/data/Psilomelane.shtml Webmineral]
* [http://mineral.galleries.com/minerals/oxides/psilomel/psilomel.htm Mineral galleries]
<br>
[[Image:PsilomelaneMoneycClip.JPG|thumb|left|Polished '''psilomelane''' mounted on a money clip.]]
<br>
{{Manganese minerals}}
[[Category:Barium minerals]]
[[Category:Manganese minerals]]
[[Category:Oxide minerals]]
[[nl:Psilomelaan]]
[[ru:Псиломелан]]
[[sk:Psilomelán]]
[[sl:Psilomelan]]