alluaudite

{{Short description|Relatively common alkaline manganese iron phosphate mineral}}

{{Infobox mineral

| name = Alluaudite

| image = Alluaudite 2 Sodium iron manganese phosphate Pleasant Valley Mine near Fourmile Custer County South Dakota 2264Spp.jpg

| alt =

| caption = Alluaudite

| category = Phosphate minerals

| formula = {{chem2|(Na,Ca)Mn^{2+}(Fe^{3+},Mn^{2+},Fe^{2+},Mg)2(PO4)3}}

|IMAsymbol=Ald{{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 =

| strunz = 8.AC.10

| dana = 38.2.3.6

| system = Monoclinic

| class = Prismatic (2/m)
(same H-M symbol)

| symmetry = C2/c

| unit cell = a = 11.03 Å, b = 12.53 Å
c = 6.4 Å; β = 97.57°; Z = 4

| color = Dirty yellow to brownish yellow, grayish green; superficially dull greenish black, brownish black, black, when altered

| habit = Platy to radiating fibrous, nodular, granular, massive

| twinning = Polysynthetic

| cleavage = Distinct/ good on {100} and {010}, good on {110}

| fracture =

| tenacity =

| mohs = 5 – 5.5

| luster =

| streak = Brownish yellow

| diaphaneity = Translucent

| gravity = 3.4 – 3.5

| density =

| polish =

| opticalprop = Biaxial (+)

| refractive = n_α = 1.782 n_β = 1.802 n_γ = 1.835

| birefringence = δ = 0.053

| pleochroism = X = pale olive-green, straw-yellow to greenish yellow; Z = pale olive-greenish to brownish yellow

| 2V = Measured: 50° to 90°, calculated: 78°

| dispersion =

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| references = [http://www.webmineral.com/data/Alluaudite.shtml#.VTekNNK6fRY Alluaudite data on Webmineral]

}}

Alluaudite is a relatively common alkaline manganese iron phosphate mineral with the chemical formula {{chem2|(Na,Ca)Mn^{2+}(Fe^{3+},Mn^{2+},Fe^{2+},Mg)2(PO4)3}}. It occurs as metasomatic replacement in granitic pegmatites and within phosphatic nodules in shales.

It was first described in 1848 for an occurrence in Skellefteå, Västerbotten, Sweden. It was named by Alexis Damour after François Alluaud (II) (1778–1866).[http://www.mindat.org/min-142.html Alluaudite on Mindat.org]{{Cite web |url=http://www.handbookofmineralogy.org/pdfs/alluaudite.pdf |title=Alluaudite in the Handbook of Mineralogy |access-date=2009-12-21 |archive-date=2016-03-03 |archive-url=https://web.archive.org/web/20160303205227/http://www.handbookofmineralogy.org/pdfs/alluaudite.pdf |url-status=dead }} The mineral structure was first described in 1955.{{Cite journal |last1=Nowagiel |first1=Maciej |last2=Samsel |first2=Mateusz J. |last3=Pietrzak |first3=Tomasz K. |date=2021-09-01 |title=Towards the High Phase Purity of Nanostructured Alluaudite-Type Glass-Ceramics Cathode Materials for Sodium Ion Batteries |journal=Materials |volume=14 |issue=17 |pages=4997 |doi=10.3390/ma14174997 |pmc=8434363 |pmid=34501086|bibcode=2021Mate...14.4997N |doi-access=free }}