Pyroxferroite

{{Short description|Single chain inosilicate mineral}} {{Infobox mineral | name = Pyroxferroite | category = Inosilicate minerals (single chain) | group = Pyroxene group | series = Pyroxferroite-Pyroxmangite series | boxwidth = | image = Pyroxferroite.jpg | caption = Pyroxferroite | formula = (Fe²⁺,Ca)SiO₃ | IMAsymbol = Pxf<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> | strunz = 9.DO.05 | system = Triclinic | symmetry = P{{overline|1}} (no. 2) | unit cell = a = 6.6213&nbsp;Å, <br/>b = 7.5506&nbsp;Å, <br/>c = 17.3806&nbsp;Å, <br/>α = 114.267°, β = 82.684°, γ = 94.756°, Z&nbsp;=&nbsp;14 | color = Yellow | habit = | twinning = | cleavage = Good on (010), poor on (001) | fracture = | mohs = 4.5–5.5 | luster = Vitreous | opticalprop = Biaxial (+) | refractive = n_α = 1.748–1.756 <br/>n_β = 1.750–1.758 <br/>n_γ = 1.767–1.768 | 2V = 34–40° | birefringence = | pleochroism = Faint; pale yellow to yellow-orange | streak = White | gravity = 3.68–3.76 g/cm³ (measured) | melt = | fusibility = | solubility = | other = | references =<ref name = handbook>{{cite web|url=http://rruff.geo.arizona.edu/doclib/hom/pyroxferroite.pdf|title=Pyroxferroite|publisher=Handbook of Mineralogy|accessdate=2009-08-07}}</ref><ref name=mindat>{{cite web|url=http://www.mindat.org/min-3326.html |title=Pyroxferroite|publisher=Mindat.org|accessdate=2010-08-07}}</ref><ref name=webmin>{{cite web|url=http://webmineral.com/data/Pyroxferroite.shtml|title=Pyroxferroite|publisher=Webmineral|accessdate=2010-08-07}}</ref><ref name=j3>{{cite journal|title=Pyrox-ferrite, a new calcium-bearing iron silicate from Tranquillity Base|author=Chao, E. C. T.|journal=Geochimica et Cosmochimica Acta Supplement |volume=1 |year=1970|page=65|url=http://adsabs.harvard.edu/full/1970GeCAS...1...65C|bibcode=1970GeCAS...1...65C|display-authors=etal}}</ref><ref>{{cite journal |last1=Windley |first1=B.F. |year=1973 |title=Proceedings of the Second Lunar Science Conference |journal= Journal of Geology|volume=81 |number=4 |pages=523–524|doi=10.1086/627901 |bibcode=1973JG.....81..523W }}</ref> }}

'''Pyroxferroite''' (Fe²⁺,Ca)SiO₃ is a single chain inosilicate. It is mostly composed of iron, silicon and oxygen, with smaller fractions of calcium and several other metals.<ref name = handbook/> Together with armalcolite and tranquillityite, it is one of the three minerals which were discovered on the Moon during the 1969 Apollo 11 mission. It was then found in Lunar and Martian meteorites as well as a mineral in the Earth's crust. Pyroxferroite can also be produced by annealing synthetic clinopyroxene at high pressures and temperatures. The mineral is metastable and gradually decomposes at ambient conditions, but this process can take billions of years.

==Etymology== Pyroxferroite is named from ''pyroxene'' and ''ferrum'' (Latin for iron), as the iron-rich analogue of pyroxmangite.<ref name=handbook/> The word pyroxene, in turn comes from the Greek words for ''fire'' (πυρ) and ''stranger'' (ξένος). Pyroxenes were named this way because of their presence in volcanic lavas, where they are sometimes seen as crystals embedded in volcanic glass; it was assumed they were impurities in the glass, hence the name "fire strangers". However, they are simply early-forming minerals that crystallized before the lava erupted.<ref>[https://books.google.com/books?id=qYHPuEwaBswC&pg=PA757 Concise English Dictionary], Wordsworth Editions, 2007 {{ISBN|1-84022-497-5}} p. 757</ref><ref>William Alexander Deer, Robert Andrew Howie, J. Zussman [https://books.google.com/books?id=x0_kPGjeYcMC&pg=PA3 Single-chain silicates, Volume 2], Geological Society, 1997, {{ISBN|1-897799-85-3}}, p. 3</ref>

==Occurrence== Pyroxferroite was first discovered in 1969 in lunar rock samples from Tranquility Base, the Sea of Tranquility landing site of Apollo 11.<ref name=j3/> Together with armalcolite and tranquillityite, it is one of the three minerals which were first found on the Moon.<ref>[http://curator.jsc.nasa.gov/lunar/letss/Mineralogy.pdf Lunar Sample Mineralogy], NASA</ref> Later, pyroxferroite was detected in Lunar and Martian meteorites recovered in Oman. It also occurs in the Earth's crust, in association with clinopyroxene, plagioclase, ilmenite, cristobalite, tridymite, fayalite, fluorapatite and potassic feldspar, and forms series with pyroxmangite. Pyroxferroite has been found in the Isanago mine, in Kyoto Prefecture, Japan; near Iva, Anderson County, South Carolina, US; from Väster Silfberg, Värmland, Sweden; and Lapua, Finland.<ref name=handbook/><ref name=mindat/> In the original lunar samples, pyroxferroite was associated with similar minerals, but also with troilite which is rare on Earth, but is common on the Moon and Mars.<ref name=j3/>

==Synthesis== Synthetic pyroxferroite crystals can be produced by compressing synthetic clinopyroxene (composition Ca_0.15Fe_0.85SiO₃) to a pressure in the range of 10–17.5 kbar and heating it to 1130–1250&nbsp;°C. It is metastable at low temperatures and pressures: at pressures below 10 kbar pyroxferroite converts to a mixture of olivine, pyroxene and a silicon dioxide phase, whereas at low temperatures, it transforms to a clinopyroxene.<ref name=j3/> The presence of cristobalite, vesicular texture and some other petrographic observations indicate that the lunar pyroxferroite was produced upon rapid cooling from low-pressure and high-temperature (volcanic) conditions, i.e. that the mineral is metastable. However, the conversion rate is very slow and pyroxferroite can exist at low temperatures for periods longer than 3 billion years.<ref>{{cite journal|doi=10.1126/science.168.3929.364|last1=Lindsley|pmid=17809134|year=1970|first1=D. H.|pages=364–7|issue=3929|volume=168|last2=Burnham|journal=Science|first2=C. W. |title=Pyroxferroite: Stability and X-ray Crystallography of Synthetic Ca0.15Fe0.85SiO3 Pyroxenoid |bibcode = 1970Sci...168..364L |s2cid=6554378}}</ref>

thumb|Crystal structure. Colors: blue – Fe, gray – Si, red – oxygen.

==Properties== The crystal structure of pyroxferroite contains silicon-oxygen chains with a repeat period of seven SiO₄ tetrahedra. These chains are separated by polyhedra where a central metal atom is surrounded by 6 or 7 oxygen atoms; there are 7 inequivalent metal polyhedra in the unit cell. The resulted layers are parallel to (110) planes in pyroxferroite, whereas they are parallel to (100) planes in pyroxenes.<ref>{{cite journal|title=The crystal structure of pyroxferroite from Mare Tranquillitatis|author=Burnham, C. W.|journal=Proceedings of the Lunar Science Conference|year=1971| volume= 2|page=47|bibcode=1971LPSC....2...47B}}</ref>

Chemical composition of pyroxferroite can be decomposed into elementary oxides as follows: FeO (concentration 44–48%), SiO₂(45–47%), CaO (4.7–6.1%), MnO (0.6–1.3%), MgO (0.3-1%), TiO₂ (0.2–0.5%) and Al₂O₃ (0.2–1.2%). Whereas magnesium is usually present at about 0.8%, in some samples it had an undetectably low concentration.<ref name=j3/>

==References== {{Reflist|25em}}

{{Manganese minerals}}

Category:Iron(II) minerals Category:Manganese(II) minerals Category:Calcium minerals Category:Pyroxene group Category:Triclinic minerals Category:Minerals in space group 2 Category:Apollo 11 Category:Minerals described in 1970