Mimetite Explained

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Mimetite
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Category:Arsenate minerals
Apatite group
Formula:Pb5(AsO4)3Cl
Imasymbol:Mim[1]
Strunz:8.BN.05
System:Hexagonal
Class:Dipyramidal (6/m)
(same H-M symbol)
Symmetry:P63/m
Unit Cell:a = 10.250(2) Å,
c = 7.454(1) Å; Z = 2
Color:Pale to bright yellow, yellowish brown, yellow-orange, white, may be colorless
Habit:Prismatic to acicular crystals; reniform, botryoidal, globular,
Twinning:Rare on
Cleavage:[10{{overline|1}}1] Imperfect
Fracture:Brittle, conchoidal
Tenacity:Brittle
Mohs:3.5–4
Luster:Resinous, subadamantine
Refractive:nω = 2.147 nε = 2.128
Opticalprop:Uniaxial (−), anomalously biaxial
Birefringence:0.019
Pleochroism:Weak
Streak:White
Gravity:7.1–7.24
Diaphaneity:Transparent to translucent
References:[2] [3]

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. 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 and with vanadinite . Notable occurrences are Mapimi, Durango, Mexico and Tsumeb, Namibia.

Properties

Mimetite is a lead chloride arsenate mineral with the composition . It is a secondary mineral, formed by oxidation of primary lead minerals in arsenic-bearing lead deposits.[2] It 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.[4]

Mimetite forms a complete solid solution series with pyromorphite, with phosphate substituting for arsenate . 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.[4] 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

Mimetite is found in association with lead and arsenic minerals, including pyromorphite, cerussite, hemimorphite, smithsonite, vanadinite, anglesite, pyrite, mottramite, willemite, and wulfenite.[4] [2] Good specimens have been reported from Gila County, Arizona, US; Ojocaliente, Zacatecas, Mexico; Cumberland, England; Johanngeorgenstadt, Saxony, Germany; Namibia; and Broken Hill, Australia.[4]

External links

Notes and References

  1. Warr. L.N.. 2021. IMA–CNMNC approved mineral symbols. Mineralogical Magazine. 85. 3. 291–320. 10.1180/mgm.2021.43. 2021MinM...85..291W. 235729616. free.
  2. Book: John W. . Anthony . Richard A. . Bideaux . Kenneth W. . Bladh . Monte C. . Nichols . Handbook of Mineralogy . Mineralogical Society of America . Chantilly, VA 20151-1110, US. 12 February 2022.
  3. Web site: Barthelmy . David . Mimetite Mineral Data . Mineralogy Database . Webmineral.com . 12 February 2022 . 2014.
  4. Book: Sinkankas . John . Mineralogy for amateurs. . 1964 . Van Nostrand . Princeton, N.J. . 0442276249 . 419–422.
  5. Book: Sinkankas . John . Mineralogy for amateurs. . 1964 . Van Nostrand . Princeton, N.J. . 0442276249 . 419–422.
  6. Burke . E.A.J. . A mass discreditation of GQN minerals . The Canadian Mineralogist . 2006 . 44 . 6 . 1557–1560. 10.2113/gscanmin.44.6.1557 . 2006CaMin..44.1557B .