Marshite

{{Short description|Isometric halide mineral}}

{{Infobox mineral

| name = Marshite

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| image = Marshite.jpg

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| caption = Exceptionally well crystallized specimen of the rare copper iodide marshite from the Rubtsovskoe Deposit, Altaiskii Krai, Western Siberia, Russian Federation.

| category = Halide mineral

| formula = CuI

| IMAsymbol = Msh{{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}}

| strunz = 3.AA.05

| dana = 9.1.7.3

| system = Isometric

| class = Hextetrahedral ({{overline|4}}3m)

| symmetry = F{{overline|4}}3m

| unit cell = a = 6.05 Å (untwinned a = 6.6063(1) Å); Z=4

| color = Honey-yellow, exposed to air pink-red to brick-red

| habit = Tetrahedral crystals, cubo-octahedral, crusts

| twinning = On {111}

| cleavage = {011} perfect

| fracture = Conchoidal

| tenacity = Brittle

| mohs = 2.5

| luster = Adamantine, greasy

| streak = Yellow

| diaphaneity = Transparent

| gravity = 5.68

| density = 5.68 g/cm³ (measured),
5.71 g/cm³ (calculated)

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| opticalprop = Isotropic

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| fluorescence = Dark red (SW, LW)

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| references = Cooper, M.A., and Hawthorne, F.C. (1997) [https://pubs.geoscienceworld.org/canmin/article-abstract/35/3/785/12901/A-note-on-the-crystal-structure-of-marshite?redirectedFrom=fulltext “A note on the crystal structure of marshite”], The Canadian Mineralogist, 35: 785–786.

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Marshite (CuI) is a naturally occurring isometric halide mineral with occasional silver (Ag) substitution for copper (Cu).Prior, G.T. (1902) [https://www.cambridge.org/core/journals/mineralogical-magazine-and-journal-of-the-mineralogical-society/article/identity-of-kilbriekenite-with-geocronite-and-analyses-of-miersite-marshite-and-copperpyrites/ED438438E066B72927A894C1ED942B8C “The identity of kilbrickenite with geocronite: And analyses of miersite, marshite, and copper-pyrites”], Mineralogical Magazine, 13: 186–190.Palache, C., Berman, H., Frondel, C. (1951) "The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana Yale University 1837-1892, Volume II: Halides, Nitrates, Borates, Carbonates, Sulfates, Phosphates, Arsenates, Tungstates, Molybdates, Etc." John Wiley and Sons, Inc., New York, 7th edition, revised and enlarged: pp. 20-22. Solid solution between the silver end-member miersite and the copper end-member marshite has been found in these minerals from deposits in Broken Hill, Australia.Millsteed, P.W. (1998) [https://pubs.geoscienceworld.org/minmag/article-abstract/62/4/471/85159/Marshite-miersite-solid-solution-and-iodargyrite?redirectedFrom=fulltext “Marshite - miersite solid solution and iodargyrite from Broken Hill, New South Wales, Australia“]. Mineralogical Magazine, 62(4): 471–475. The mineral's name is derived from the person who first described it, an Australian mineral collector named Charles W. Marsh.[http://www.handbookofmineralogy.com/pdfs/marshite.pdf Handbook of Mineralogy - Marshite][http://www.mindat.org/min-2580.html Mindat.org - Marshite][http://webmineral.com/data/Marshite.shtml Webmineral - Marshite] Marsh drew attention to native copper iodide (Marshite) in the 1800s emphasizing its natural occurrence, it is not to be confused with copper (I) iodide a substance commonly synthesized in laboratory settings.Marsh, C.W. (1892) Proceedings of the Royal Society of New South Wales, 26: 326–332 (as Native copper iodide).Marsh, C.W. and Liversidge, A. (1892) "On Native Copper Iodide (Marshite) and other Minerals from Broken Hill, N.S. Wales", Journal and Proceedings of the Royal Society of New South Wales, 26: 326–332.

One of marshite's distinguishing features is that prior to exposure to air the mineral is a faint honey-yellow color, once exposed to the air however it becomes a brick-red color. Another characteristic useful in identifying marshite is the dark red color it fluoresces under short-wave (SW) and long-wave (LW) ultraviolet light.