{{Short description|Manganese iron oxide mineral}} {{Infobox mineral | name = Jacobsite | category = Oxide minerals <br />Spinel group <br />Spinel structural group | boxwidth = | image = Jacobsite-cktsr-15a.jpg | imagesize = 260px | caption = | formula = iron(II,III) manganese oxide, (Mn,Mg)Fe<sub>2</sub>O<sub>4</sub> | IMAsymbol = Jcb<ref>{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|journal=Mineralogical Magazine|volume=85|issue=3|pages=291–320|doi=10.1180/mgm.2021.43|bibcode=2021MinM...85..291W|s2cid=235729616|doi-access=free}}</ref> | molweight = | strunz = 4.BB.05 | system = Isometric | class = Hexoctahedral (m{{overline|3}}m) <br/>H-M symbol: (4/m {{overline|3}} 2/m) | symmetry = ''Fd{{overline|3}}m'' (no. 227) | unit cell = a = 8.457 Å; Z = 8 | color = Black to brownish black | habit = Disseminated to massive, rarely as octahedral crystals | twinning = Spinel law, flattened on {111} or lamellar | cleavage = {111}, probably a parting | fracture = Conchoidal | mohs = 5.5–6.5 | luster = Metallic | refractive = ~2.3 | opticalprop = Isotropic | birefringence = | pleochroism = | streak = reddish black to brown | gravity = 4.76 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Opaque | other = weakly magnetic | references = <ref name=Handbook>[http://rruff.geo.arizona.edu/doclib/hom/jacobsite.pdf Handbook of Mineralogy]</ref><ref name=Mindat>[http://www.mindat.org/min-2061.html Mindat.org]</ref> }}
'''Jacobsite''' is a manganese iron oxide mineral. It is in the spinel group and forms a solid solution series with magnetite. The chemical formula is (Mn,Mg)Fe<sub>2</sub>O<sub>4</sub> or with oxidation states and substitutions: (Mn<sup>2+</sup>,Fe<sup>2+</sup>,Mg)(Fe<sup>3+</sup>,Mn<sup>3+</sup>)<sub>2</sub>O<sub>4</sub>.<ref name=Handbook/><ref name=Webmin>[http://www.webmineral.com/data/Jacobsite.shtml Webmineral data] </ref> [[File:Jacobsite-d05-134a.jpg|thumb|left|Jacobsite, N'Chwaning Mines, Kuruman, Kalahari manganese fields, Northern Cape Province, South Africa. Size 3.8 x 3.5 x 3.2 cm]] {{clear left}} It occurs as a primary phase or as alteration of other manganese minerals during metamorphism of manganese deposits.<ref name=Webmin/> Typical associated minerals include hausmannite, galaxite, braunite, pyrolusite, coronadite, hematite and magnetite.<ref name=Handbook/> It is a ferrimagnetic substance, which is weakly attracted by a magnet.
It was first described in 1869 and named for the Jakobsberg Mine, Nordmark, Filipstad, Värmland, Sweden.<ref name=Mindat/>
==References== {{Reflist}}
*[https://web.archive.org/web/20060301151751/http://www.npi.gov.au/database/substance-info/profiles/52.html National Pollutant Inventory - Manganese and compounds Fact Sheet]
{{-}} Category:Spinel group Category:Iron(II,III) minerals Category:Manganese(II,III) minerals Category:Magnesium minerals Category:Magnetic minerals Category:Cubic minerals Category:Minerals in space group 227 Category:Minerals described in 1869
{{oxide-mineral-stub}} {{Manganese minerals}}