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]]