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Pyroxferroite

Field	Value
name	Pyroxferroite
category	Inosilicate minerals (single chain)
group	Pyroxene group
series	Pyroxferroite-Pyroxmangite series
image	Pyroxferroite.jpg
caption	Pyroxferroite
formula	(Fe2+,Ca)SiO3
IMAsymbol	Pxf
strunz	9.DO.05
system	Triclinic
symmetry	P (no. 2)
unit cell	a = 6.6213 Å,
b = 7.5506 Å,
c = 17.3806 Å,
α = 114.267°, β = 82.684°, γ = 94.756°, Z = 14
color	Yellow
cleavage	Good on (010), poor on (001)
mohs	4.5–5.5
luster	Vitreous
opticalprop	Biaxial (+)
refractive	nα = 1.748–1.756
nβ = 1.750–1.758
nγ = 1.767–1.768
2V	34–40°
pleochroism	Faint; pale yellow to yellow-orange
streak	White
gravity	3.68–3.76 g/cm3 (measured)
references

b = 7.5506 Å, c = 17.3806 Å, α = 114.267°, β = 82.684°, γ = 94.756°, Z = 14 nβ = 1.750–1.758 nγ = 1.767–1.768

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. 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.

Occurrence

Pyroxferroite was first discovered in 1969 in lunar rock samples from Tranquility Base, the Sea of Tranquility landing site of Apollo 11. 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. 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.

Synthesis

Synthetic pyroxferroite crystals can be produced by compressing synthetic clinopyroxene (composition Ca0.15Fe0.85SiO3) to a pressure in the range of 10–17.5 kbar and heating it to 1130–1250 °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.

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.

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.

References

Warr, L.N.. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine.
"Pyroxferroite". Handbook of Mineralogy.
"Pyroxferroite". Mindat.org.
"Pyroxferroite". Webmineral.
Chao, E. C. T.. (1970). "Pyrox-ferrite, a new calcium-bearing iron silicate from Tranquillity Base". Geochimica et Cosmochimica Acta Supplement.
(1973). "Proceedings of the Second Lunar Science Conference". Journal of Geology.
1-84022-497-5 p. 757
1-897799-85-3, p. 3
Together with [[armalcolite]] and [[tranquillityite]], it is one of the three minerals which were first found on the Moon.[http://curator.jsc.nasa.gov/lunar/letss/Mineralogy.pdf Lunar Sample Mineralogy], NASA
Burnham, C. W.. (1971). "The crystal structure of pyroxferroite from Mare Tranquillitatis". Proceedings of the Lunar Science Conference.

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iron(ii)-minerals manganese(ii)-minerals calcium-minerals pyroxene-group triclinic-minerals minerals-in-space-group-2 apollo-11 minerals-described-in-1970

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