hercynite

{{Infobox mineral

| name = Hercynite

| category = Oxide minerals
Spinel group
Spinel structural group

| boxwidth =

| image = Hercynite.jpg

| imagesize = 260px

| caption =

| formula = Fe²⁺Al₂O₄

| IMAsymbol = Hc{{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}}

| molweight = 173.81 g/mol

| strunz = 4.BB.05

| system = Isometric

| class = Hexoctahedral (m{{overline|3}}m)
H-M symbol: (4/m {{overline|3}} 2/m)

| symmetry = Fd{{overline|3}}m (no. 227)

| color = Black

| habit = Euhedral crystals. Also massive to granular

| cleavage = [111] indistinct

| fracture = Uneven – flat surfaces (not cleavage) fractured in an uneven pattern.

| mohs = 7.5

| luster = Vitreous (glassy)

| refractive = n = 1.8

| opticalprop = Isotropic

| birefringence =

| pleochroism =

| streak = dark green

| gravity = 3.95

| melt =

| fusibility =

| diagnostic =

| solubility =

| diaphaneity =

| other = non-radioactive

| references = [http://www.handbookofmineralogy.com/pdfs/hercynite.pdf Handbook of Mineralogy][http://webmineral.com/data/Hercynite.shtml Webmineral][http://www.mindat.org/min-1875.html Mindat]

}}

Hercynite is a spinel mineral with the formula FeAl₂O₄.

It occurs in high-grade metamorphosed iron-rich argillaceous (clay-containing) sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers.

It was first described in 1847 and its name originates from the Latin name for the Harz, Silva Hercynia, where the species was first found.

Hercynite is a spinel of regular symmetry and normal cation distribution, but some disorder occurs in its structure. It consists of ferrous (Fe²⁺) ions and aluminium ions (Al³⁺); however some ferric ions (Fe³⁺) may be located in the structure of hercynite.{{Cite journal|title = Crystal structure and Mössbauer study of FeAl2O4|last1 = Jastrzębska|first1 = Ilona|journal = Nukleonika-Journal of Nuclear Research|doi = 10.1515/nuka-2015-0012|last2 = Szczerba J.|publisher = Institute of Nuclear Chemistry and Technology|issue = 1|year = 2015|department = Department of Ceramics and Refractories|pages = 47–49|last3 = Stoch P.|last4 = Błachowski A.|last5 = Ruebenbauer K.|last6 = Prorok R.|last7 = Snieżek E.|volume = 60|doi-access = free}}

Melting point of this mineral is inbetween {{convert|1692-1767|C|F}}.{{Cite journal |last1=Agca |first1=Can |last2=Neuefeind |first2=Jörg C. |last3=McMurray |first3=Jake W. |last4=Weber |first4=Richard |last5=Navrotsky |first5=Alexandra |date=2020-06-07 |title=Melting temperature measurement of refractory oxide ceramics as a function of oxygen fugacity using containerless methods |url=http://dx.doi.org/10.1111/jace.17216 |journal=Journal of the American Ceramic Society |volume=103 |issue=9 |pages=4867–4875 |doi=10.1111/jace.17216 |osti=1648884 |s2cid=219429990 |issn=0002-7820}}