Mimetite

Mimetite
General
Category	Arsenate minerals
Chemical formula	Pb5(AsO4)3Cl lead chloro-arsenate
Strunz classification	08.BN.05
Identification
Color	Yellow, Brown, Orange, Red, White
Crystal habit	Reniform, botryoidal, globular, prismatic
Crystal system	Hexagonal
Cleavage	[1011] Imperfect
Fracture	Brittle, conchoidal
Mohs scale hardness	3.5 - 4
Luster	Resinous, adamantine
Streak	White
Diaphaneity	Subtransparent to translucent
Specific gravity	7.1 - 7.24
Refractive index	2.129 - 2.144

Mimetite, whose name derives from the Greek Μιμητής mimethes, meaning "imitator", is an arsenate mineral which forms as a secondary mineral in lead deposits, usually by the oxidation of galena and arsenopyrite. The name is a reference 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). The most notable occurrences are Mapimi, Durango, Mexico and Tsumeb, Namibia.

Uses of mimetite

Mimetite from Namibia

Industrially, mimetite is a minor ore of lead, especially when found in relatively large quantities. The chief use of mimetite is as a collector's specimen, often creating very attractive botryoidal crusts on the surface of the specimen. Though mimetite is also found in prismatic crystal forms, it is not used as a gemstone due to its softness. The best of these prismatic forms have been found in Johanngeorgenstadt in Saxony and Wheal Unity in Cornwall, England.

Associated minerals

Mimetite is found in association with lead and arsenic minerals, including those minerals with which it forms a series. Some associated minerals include:

• Bellite
• Calcite, CaCO₃
• Galena, PbS
• Pyromorphite, Pb₅(PO₄)₃Cl
• Smithsonite, ZnCO₃
• Vanadinite, Pb₅(VO₄)₃Cl
• Wulfenite, PbMoO₄

Alternative names

Alternative names of mimetite include arsenopyromorphite, mimetesite, and prixite. Campylite is the name for a variety with barrel shaped crystals of a brownish-red or orange-yellow color and containing a considerable proportion of phosphoric acid.

Notes for identification

Useful information pertaining to the field identification of mimetite include its habit, color, and high density. However, this mineral's similarity to pyromorphite can be problematic, especially since these minerals are known to share colors. Pyromorphite is typically green, and mimetite is typically yellow, but specimens of each are known in the other's colors. As a result, some identification may require lab analysis.

Mimetite specimen gallery

• 

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

• 

  Mimetite, Santa Eulalia, Chihuahua, Mexico. Size: 5.4 x 3.9 x 1.5 cm.

• 

  Mimetite, Bilbao mine, Zacatecas, Mexico. Size: 7.9 x 5.8 x 3.4 cm.

• 

  A thumbnail sample of mimetite.

References

• WebMineral Listing
• MinDat Listing
• Mineral Galleries