Laurionite

{{Short description|Lead halide mineral}}

{{infobox mineral

| name = Laurionite

| boxwidth =

| boxbgcolor =

| image = Laurionite-154998.jpg

| imagesize =

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| caption = Laurionite crystals in a vug from the Laurium district of Greece

| category = Halide minerals

| formula = PbCl(OH)

| IMAsymbol = Lri{{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 = 3.DC.05

| dana =

| system = Orthorhombic

| class = Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)

| symmetry = Pnma

| unit cell = a = 7.111, b = 9.6987
c = 4.0203 [Å]; Z = 4

| color = Colorless, white

| colour =

| habit = Elongated tabular prismatic crystals

| twinning =

| cleavage = Distinct on {101}

| fracture =

| tenacity = Flexible

| mohs = 3–3.5

| luster = Adamantine, pearly

| streak = White

| diaphaneity = Transparent

| gravity = 6.241

| density =

| polish =

| opticalprop = Biaxial (−)

| refractive = n_α = 2.077 n_β = 2.116 n_γ = 2.158

| birefringence = δ = 0.081

| pleochroism =

| 2V = Measured: 70°

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| diagnostic =

| solubility = Sleight in cold water

| impurities =

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| references = [http://www.mindat.org/min-2343.html Mindat.org][http://rruff.geo.arizona.edu/doclib/hom/laurionite.pdf Handbook of Mineralogy][http://www.webmineral.com/data/Laurionite.shtml Webmineral data for laurionite][https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Laurionite Mineralienatlas]

}}

Laurionite (PbCl(OH)) is a lead halide mineral. It forms colorless to white crystals in the orthorhombic crystal system and is dimorphous with paralaurionite, both members of the matlockite group.

It was first described in 1887 for an occurrence in the Laurium District, Attica, Greece, and named after the town Laurium.

It occurs as an oxidation product in lead ore deposits, and is also produced on lead-bearing slag by reaction with saline solutions. It occurs associated with paralaurionite, penfieldite, fiedlerite, phosgenite, cerussite and anglesite.