# Mendipite

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> Source: https://en.wikipedia.org/wiki/Mendipite
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{{short description|Oxyhalide of lead. Rare mineral found in the Mendip Hills}}
{{Infobox mineral
| name = Mendipite
| category = [Halide mineral](/source/Halide_mineral)
| boxwidth =
| boxbgcolor =
| image = Mendipite-160217.jpg
| imagesize   = 220px
| caption =
| formula = Pb<sub>3</sub>Cl<sub>2</sub>O<sub>2</sub>
| IMAsymbol   = Mdi<ref>{{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}}</ref>
| molweight = 724.50 g/mol
| strunz = 3.DC.70 Oxyhalide
| dana = 10.3.1.1
| system = [Orthorhombic](/source/Orthorhombic)
| class = Dipyramidal (mmm) <br/>[H-M symbol](/source/H-M_symbol): (2/m 2/m 2/m)
| symmetry =  ''Pnma''<ref name = Dana /><ref name = atlas /> <br><small>or ''P2''<sub>1</sub>2<sub>1</sub>2<sub>1</sub>,<ref name = Mindat /><ref name = Webmin /><ref name = HOM /></small>
| unit cell = a = 9.52&nbsp;Å, b = 11.87&nbsp;Å, <br/>c = 5.87&nbsp;Å; Z&nbsp;=&nbsp;4
| color = Colorless to white, brownish cream, grey, yellowish, pink, red, or blue; nearly colorless in transmitted light.
| habit = Columnar or fibrous aggregates, often radiated, and cleavable masses.
| twinning =
| cleavage = Perfect on {110}, fair on {100} and {010}
| fracture = Conchoidal to uneven
| tenacity =
| mohs = {{frac|2|1|2}} to 3
| luster = Pearly to silky on cleavages; resinous to adamantine on fractures.
| refractive = n<sub>α</sub> = 2.240, n<sub>β</sub> = 2.270, n<sub>γ</sub> = 2.310
| opticalprop = Biaxial (+)
| birefringence = δ = 0.070
| pleochroism =
| 2V = Measured: 90°, calculated: 84°
| streak = White
| gravity = 7.24<ref name = Mindat /><ref name = HOM /><ref name = Dana />
| melt =
| fusibility =
| diagnostic =
| solubility = Soluble in dilute [nitric acid](/source/nitric_acid), HNO<sub>3</sub>
| diaphaneity = Translucent, rarely transparent
| other =
| references = <ref name=atlas>[https://www.mineralienatlas.de/lexikon/index.php/MineralData?mineral=Mendipite Mineralienatlas]</ref><ref name = Mindat>{{cite web|url=http://www.mindat.org/min-2641.html|title=Mendipite|website=MinDat.org}}</ref><ref name = Webmin>{{cite web|url=http://www.webmineral.com/data/Mendipite.shtml|title=Mendipite Mineral Data|author=Dave Barthelmy|website=WebMineral.com|access-date=2015-01-04}}</ref><ref name = HOM>{{cite web|url=http://www.handbookofmineralogy.org|title=Handbook of Mineralogy|publisher=}}</ref><ref name = Dana>Gaines et al (1997) Dana’s New Mineralogy Eighth Edition. Wiley</ref> }}

'''Mendipite''' is a rare mineral that was named for the locality where it is found, the [Mendip Hills](/source/Mendip_Hills) in Somerset, England. It is an [oxyhalide](/source/oxyhalide) of [lead](/source/lead) with formula Pb<sub>3</sub>Cl<sub>2</sub>O<sub>2</sub>.<ref name = Mindat/>

== Crystal structure ==
Most references assert that mendipite crystallises in the [orthorhombic crystal system](/source/orthorhombic_crystal_system), [disphenoid](/source/disphenoid)al class 2 2 2, meaning that it has three mutually perpendicular [axes of twofold symmetry](/source/Rotational_symmetry), with [space group](/source/space_group) P2<sub>1</sub>2<sub>1</sub>2<sub>1</sub>, meaning that each of these axes is a [screw axis](/source/screw_axis).<ref name = Mindat /><ref name = Webmin /><ref name = HOM /> One reference, however, gives the crystal class as orthorhombic m m m with space group Pnma,<ref name = Dana /> which has a higher symmetry. In each case the "P" means that the mineral has a [primitive unit cell](/source/Unit_cell).

[Unit cell](/source/Unit_cell) parameters:
* a = 9.52 Å, b = 11.87 Å, c = 5.87 Å, Z = 4<ref name = Mindat /><ref name = Webmin /><ref name = HOM />
* a = 11.87 Å, b = 5.806 Å, c = 9.48 Å, Z = 4<ref name = Dana />

== Optical properties ==
Mendipite is colorless to white, brownish cream, grey, yellowish, pink, red, or blue. It is nearly colorless in transmitted light. It has a white [streak](/source/Streak_(mineralogy)) and its [luster](/source/Lustre_(mineralogy)) is pearly to silky on cleavages, and resinous to adamantine on fractures. The mineral is translucent, and rarely transparent. It is [biaxial (+)](/source/Birefringence), with [refractive indices](/source/Refractive_index) N<sub>x</sub> = 2.24, N<sub>y</sub> = 2.27, N<sub>z</sub> = 2.31. These values are quite high, compared with ordinary glass at 1.5. This is typical of [lead](/source/lead) minerals.

== Physical properties ==
Mendipite is found in columnar or fibrous aggregates, often radiated but more rarely straight long fibers, and in cleavable masses. The [cleavage](/source/Cleavage_(mineralogy)) is perfect on {110} and fair on {100} and {010}. [Fracture](/source/Fracture_(geology)) is conchoidal (shell-like) to uneven and the mineral is soft, with [hardness](/source/Mohs_hardness) only {{frac|2|1|2}} to 3, a bit less than that of [calcite](/source/calcite). Because of the [lead](/source/lead) content the [specific gravity](/source/specific_gravity) is high, at 7.24,<ref name = Mindat /><ref name = HOM /><ref name = Dana /> or 7 to 7.2,<ref name = Webmin /> just a little less than that of [mimetite](/source/mimetite), another lead mineral. Mendipite is soluble in dilute [nitric acid](/source/nitric_acid), HNO<sub>3</sub>.<ref name = Dana /> It is not [radioactive](/source/Radioactive_decay).<ref name = Webmin />

== Environment ==
At the Eleura Mine near [Cobar](/source/Cobar%2C_New_South_Wales), New South Wales, Australia, oxygenated [groundwater](/source/groundwater) reacted with [sulfide mineral](/source/sulfide_mineral)s during the [Cenozoic](/source/Cenozoic), forming [supergene](/source/Supergene_(geology)) sulfides, as well as the [sulfate mineral](/source/sulfate_mineral)s [beudantite](/source/beudantite), [anglesite](/source/anglesite) and [baryte](/source/baryte), together with some [mimetite](/source/mimetite) and native [silver](/source/silver). [Cerussite](/source/Cerussite) crystallised later, and later still [chloride](/source/chloride)-rich groundwaters reacted with many of these earlier minerals to form more mimetite, as well as [blixite](/source/blixite), [laurionite](/source/laurionite), mendipite and [chlorargyrite](/source/chlorargyrite).<ref name = AJM11>Australian Journal of Mineralogy (2005) 11-2:89-90</ref>

At the type locality, [galena](/source/galena) was deposited in [Carboniferous Limestone](/source/Carboniferous_Limestone) throughout the [Mendip Hills](/source/Mendip_Hills) during the late [Permian](/source/Permian) or [Triassic](/source/Triassic) Period. In the [Jurassic](/source/Jurassic) Period that followed, these deposits were exposed to the action of seawater, which deposited [manganate minerals](/source/Manganese) that reacted with the galena and adsorbed [heavy metals](/source/Heavy_metal_(chemistry)) both from the seawater and surroundings. A later event heated the deposits creating the conditions which led to the formation of the suite of unusual [secondary minerals](/source/Supergene_(geology)), including a number of rare [oxohalide](/source/oxohalide) minerals, now found at Merehead.<ref name = MM70>{{cite journal|last1=Turner|first1=R.|title=A mechanism for the formation of the mineralized Mn deposits at Merehead Quarry, Cranmore, Somerset, England| journal=Mineralogical Magazine | volume=70|issue=6|year=2006 |pages=629–653|issn=0026-461X|doi=10.1180/0026461067060359|bibcode=2006MinM...70..629T|s2cid=129918302}}</ref> The mendipite occurs in [nodules](/source/nodule_(geology)) in [manganese oxide](/source/manganese_oxide) ores, associated with [hydrocerussite](/source/hydrocerussite), [cerussite](/source/cerussite), [malachite](/source/malachite), [pyromorphite](/source/pyromorphite), [calcite](/source/calcite), [chloroxiphite](/source/chloroxiphite), [diaboleite](/source/diaboleite) and [parkinsonite](/source/parkinsonite).<ref name = HOM />

== Type locality ==
The [type locality](/source/Type_locality_(geology)) is [Churchill](/source/Churchill%2C_Somerset), Mendip Hills, Somerset, England, and type material is conserved at the [Royal Swedish Academy of Sciences](/source/Royal_Swedish_Academy_of_Sciences), Stockholm, Sweden. Other localities include Australia, Germany, Greece, Sweden, the UK and the US.

== References ==
{{Reflist}}

== External links ==
* JMol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=06898

{{Commons}}
{{Authority control}}

Category:Lead minerals
Category:Oxide minerals
Category:Halide minerals
Category:Chloride minerals
Category:Oxychlorides
Category:Geology of Somerset
Category:Mendip Hills
Category:Orthorhombic minerals
Category:Minerals in space group 19
Category:Minerals in space group 62

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Adapted from the Wikipedia article [Mendipite](https://en.wikipedia.org/wiki/Mendipite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Mendipite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.