cronstedtite

{{Short description|Silicate mineral}}

{{Infobox mineral

| name = Cronstedtite

| boxwidth =

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| image = Cronstedite France.jpg

| imagesize = 260px

| alt =

| caption = Cronstedtite – Salsigne Mine – France

| category = Silicate minerals

| formula = {{chem|Fe|2|2+|Fe|3+|(Si|,Fe|3+|O|5|)|(OH)|4}}

| IMAsymbol=Cro{{Cite journal|last=Warr|first=L.N.|date=2021|title=IMA–CNMNC approved mineral symbols|url=https://www.cambridge.org/core/journals/mineralogical-magazine/article/imacnmnc-approved-mineral-symbols/62311F45ED37831D78603C6E6B25EE0A|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 = 9.ED.15

| dana =

| system = Trigonal

| class = Ditrigonal pyramidal (3 m)
(same H-M symbol)

| symmetry = P31m (no. 157)

| unit cell = a = 5.486 Å,
c = 7.095 Å; Z = 1

| color = Black, dark brown-black, green-black

| colour =

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| twinning =

| cleavage = Perfect on {001}

| fracture =

| tenacity = Elastic

| mohs =

| luster = Sub-Metallic

| streak = Dark olive green

| diaphaneity = Translucent

| gravity = 3.34 – 3.35

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| polish =

| opticalprop = Biaxial (−)

| refractive = n_α = 1.720 n_β = 1.800 n_γ = 1.800

| birefringence = δ = 0.080

| pleochroism = Visible

| 2V =

| dispersion = r < v moderate

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| references = [http://webmineral.com/data/Cronstedtite.shtml Webmineral.com][http://www.mindat.org/min-1158.html Mindat.org][http://www.handbookofmineralogy.org/pdfs/cronstedtite.pdf American Mineralogical Society]

}}

Cronstedtite is a complex iron silicate mineral belonging to the serpentine group of minerals. Its chemical formula is {{chem|Fe|2|2+|Fe|3+|(Si|,Fe|3+|O|5|)|(OH)|4}}.

It was discovered in 1821 and named in honor of Swedish mineralogist Axel Fredrik Cronstedt (1722–1765). It has been found in Bohemia in the Czech Republic and in Cornwall, England.

Cronstedtite is a major constituent of CM chondrites, a carbonaceous chondrite group exhibiting varying degrees of aqueous alteration. Cronstedtite abundance decreases with increasing alteration.Browning et al. (1996) Geochimica et Cosmochimica Acta

File:Cronstedtite Pisani.jpg, England]]