Editing Calomel (section)

{{short description|Mercury chloride mineral}}
{{Distinguish|Calamine}}
{{Infobox mineral
| name        = Calomel
| boxwidth    = 
| boxbgcolor  = 
| image       = Calomel, Terlinguaite-222734.jpg
| imagesize   = 260px
| alt         = 
| caption     = Amber calomel crystals and bright yellow terlinguaite on [[gossan]] matrix, 3 mm. across
| category    = [[Halide minerals|Halide mineral]]
| formula     = (Hg<sub>2</sub>)<sup>2+</sup>Cl<sub>2</sub>
| IMAsymbol=Clo<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>  
| strunz      = 3.AA.30
| dana        = 
| system      = Tetragonal
| class       = Ditetragonal dipyramidal 4/mmm (4/m 2/m 2/m) - 
| symmetry    = 
| unit cell   = a = 4.4795(5) Å, c = 10.9054(9) Å; Z=4
| color       = Colorless, white, grayish, yellowish white, yellowish grey to ash-grey, brown
| habit       = Crystals commonly tabular to prismatic, equant pyramidal; common as drusy crusts,
earthy, massive.
| twinning    = Contact and penetration twins on {112}
| cleavage    = Good on {110}, uneven to imperfect on {011}
| fracture    = Conchoidal
| tenacity    = Sectile
| mohs        = 1.5
| luster      = Adamantine
| streak      = 
| diaphaneity = Transparent to translucent
| gravity     = 7.5
| polish      = 
| opticalprop = Uniaxial (+); very high [[Optical relief|relief]]
| refractive  = n<sub>ω</sub> = 1.973 n<sub>ε</sub> = 2.656
| birefringence = δ = 0.683
| pleochroism = Weak, E > O
| 2V          = 
| dispersion  = 
| extinction  = 
| length fast/slow =
| fluorescence = Brick-red under UV
| absorption  = 
| melt        = 
| fusibility  = 
| diagnostic  = 
| solubility  = 
| impurities  = 
| alteration  = 
| other       = 
| references  = <ref name=handbook/><ref name=Mindat>[https://www.mindat.org/min-869.html Calomel on Mindat]</ref><ref>[http://www.webmineral.com/data/Calomel.shtml#.WYM-3ojytPY Calomel on Webmin]</ref>
}}
'''Calomel''' is a [[Mercury element|mercury]] [[chloride]] [[mineral]] with [[Chemical formula|formula]] Hg<sub>2</sub>Cl<sub>2</sub> (see [[mercury(I) chloride]]). It was used as a medicine from the 16th to early 20th century, despite frequently causing [[mercury poisoning]] in patients.<ref>{{Cite journal |last=Davis |first=L. E |date=2000-07-01 |title=Unregulated potions still cause mercury poisoning |journal=Western Journal of Medicine |volume=173 |issue=1 |pages=19 |doi=10.1136/ewjm.173.1.19 |pmc=1070962 |pmid=10903282}}</ref>

The name derives from Greek ''kalos'' (beautiful) and ''melas'' (black) because it turns black on reaction with [[ammonia]]. This was known to [[Alchemy|alchemists]].<ref name="Mindat" />

Calomel occurs as a secondary mineral which forms as an alteration product in mercury deposits. It occurs with [[native mercury]], [[Amalgam (chemistry)|amalgam]], [[cinnabar]], mercurian [[tetrahedrite]], [[eglestonite]],  [[terlinguaite]], [[montroydite]], [[kleinite]], [[moschelite]], [[kadyrelite]], [[kuzminite]], [[chursinite]], [[kelyanite]], [[calcite]], [[limonite]] and various [[clay minerals]].<ref name=handbook>[http://www.handbookofmineralogy.org/pdfs/calomel.pdf The Handbook of Mineralogy]</ref>

The [[Type locality (geology)|type locality]] is [[Moschellandsburg]], [[Alsenz-Obermoschel]], [[Rhineland-Palatinate]], [[Germany]].<ref name=Mindat/>