Mimetite

Lead arsenate chloride mineral

Mimetite

Golden-yellow botryoidal mimetite from Congreso-León mines, Mexico

General
Category| Arsenate minerals
Apatite group
Formula| Pb5(AsO4)3Cl
IMA symbol| Mim[1]
Strunz classification| 8.BN.05
Crystal system| Hexagonal
Crystal class| Dipyramidal (6/m)
(same H-M symbol)
Space group| P63/m
Unit cell| a = 10.250(2) Å,
c = 7.454(1) Å; Z = 2
Identification
Color| Pale to bright yellow, yellowish brown, yellow-orange, white, may be colorless
Crystal habit| Prismatic to acicular crystals; reniform, botryoidal, globular,
Twinning| Rare on {1122}
Cleavage| [1011] Imperfect
Fracture| Brittle, conchoidal
Tenacity| Brittle
Mohs scale hardness| 3.5–4
Luster| Resinous, subadamantine
Streak| White
Diaphaneity| Transparent to translucent
Specific gravity| 7.1–7.24
Optical properties| Uniaxial (−), anomalously biaxial
Refractive index| nω = 2.147 nε = 2.128
Birefringence| 0.019
Pleochroism| Weak
References| [2][3][4]

Mimetite is a lead arsenate chloride mineral (Pb5(AsO4)3Cl) which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite.[2] The name derives from the Greek Μιμητής mimetes, meaning "imitator" and refers to mimetite's resemblance to the mineral pyromorphite. This resemblance is not coincidental, as mimetite forms a mineral series with pyromorphite (Pb5(PO4)3Cl) and with vanadinite (Pb5(VO4)3Cl). Notable occurrences are Mapimi, Durango, Mexico, and Tsumeb, Namibia.

## Properties

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Mimetite from Namibia

Mimetite typically forms short hexagonal crystals that are yellow to brown to orange in color, very brittle, moderately hard (Mohs hardness 3.5–4), and dense (specific gravity 7.24). It is distinctive for its lack of transparency, its resinous to adamantine luster, and its solubility in nitric acid.[5]

Mimetite forms a complete solid solution series with pyromorphite, with phosphate (PO3−
4) substituting for arsenate (AsO3−
4). The two minerals are almost identical in their properties and can be difficult to distinguish except by laboratory tests. Pyromorphite is the more common mineral at most locales.[5]

Campylite is a name applied to mimetite or pyromorphite that crystallizes as distinctive barrel-shaped crystals forming curved hemispherical aggregates.[5] Bellite is a name formerly applied to a chromium-bearing mimetite, or possibly a mixture of crocoite, mimetite, and quartz, which forms attractive orange red crystals, but has been discredited as a distinct mineral species.[6]

## Occurrences

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Mimetite is found in association with lead and arsenic minerals, including pyromorphite, cerussite, hemimorphite, smithsonite, vanadinite, anglesite, pyrite, mottramite, willemite, and wulfenite.[5][2] Good specimens have been reported from Gila County, Arizona, US; Ojocaliente, Zacatecas, Mexico; Cumberland, England; Johanngeorgenstadt, Saxony, Germany; Namibia; and Broken Hill, Australia.[5]

## Mimetite specimen gallery

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* Mimetite from Tsumeb mine, Namibia

* Cluster of translucent, golden mimetite crystals

* Spherical aggregates of botryoidal mimetite

* Mimetite, Pingtouling Mine, Guangdong Province, China. Size: 2.2 x 2.1 x 1.8 cm

## References

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1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320\. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
2. ^ a b c Anthony, John W.; Bideaux, Richard A.; Bladh, Kenneth W.; Nichols, Monte C. (eds.). Handbook of Mineralogy (PDF). Chantilly, VA: Mineralogical Society of America. Retrieved 2025-05-01.
3. ^ "Mimetite". Mindat.org. Retrieved 12 February 2021.
4. ^ Barthelmy, David (2014). "Mimetite Mineral Data". Mineralogy Database. Webmineral.com. Retrieved 12 February 2022.
5. ^ a b c d e Sinkankas, John (1964). Mineralogy for amateurs. Princeton, N.J.: Van Nostrand Reinhold. pp. 419–422\. ISBN 0442276249. `{{cite book}}`: ISBN / Date incompatibility (help)
6. ^ Burke, Ernst A.J. (2006-12-01). "A mass discreditation of GQN minerals". The Canadian Mineralogist. 44 (6): 1557–1560\. Bibcode:2006CaMin..44.1557B. doi:10.2113/gscanmin.44.6.1557.

## External links

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Wikimedia Commons has media related to Mimetite.

* "Mimetite" . Encyclopædia Britannica. Vol. 18 (11th ed.). 1911.
* Mineral Galleries