Mineral Information and Data:

Mimetite
Pb5(AsO4)3Cl [CNMNC approved formula]

Named from the Greek mimethes - "imitator" , because of its resemblance to pyromorphite. First published in 1835. Redefined per nomemclature of the apatite supergroup minerals (IMA, 2010). The name mimetite-M is used for the polymorphic variant of mimetite, previously known as clinomimetite, and is not considered a distinct species.

IMA status : Redefined IMA Approved; 2010 ()
CLASSIFICATION 
Dana
(8th edition) :
41.08.04.02  
  (41) Anhydrous Phosphates Containing Hydroxyl or Halogen
  (41.08) where (A)5 (XO4)3 Zq
  (41.08.04) Pyromorphite Group
  
Nickel-Strunz
(10th edition) :
08.BN.05
  (08) Phosphates, Arsenates, Vanadates
  (08.B) Phosphates, etc. with Additional Anions, without H2O
  (08.BN) With only large cations, (OH, etc.):RO4 = 0.33:1
  
Crystal system: Hexagonal System
Point group (H-M): 6/m — dipyramidal
Space group: P63/m
Unit cell: a = 10.250(2) Å, c = 7.454(1) Å, Z=2
Crystal Habit: Crystals are usually prismatic to acicular || [0001], to 12 cm, may be tabular, showing {1010}, {0001}, {1011}, rarely {1121}, {2131}, others; rounded, barrel-shaped, mammillary, stalactitic, granular.
Twinning: On {1122}, very rare
  
Color: Pale to bright yellow, yellowish brown, yellow-orange, white, may be colorless; colorless or pale yellow in transmitted light
Diaphaneity: Transparent to translucent
Luster: Resinous to subadamantine
Hardness (Mohs): 3.5 – 4
Measured Density: 7.24 g/cm3
Cleavage: On {1011}, interrupted
Tenacity: Brittle
Fracture: Uneven to subconchoidal
Streak: White
  
Polymorphism and Series: Mimetite-M is used for the polymorphic variant of mimetite, previously known as clinomimetite, and is not considered a distinct species (IMA, 2010)
Geologic Setting: A common secondary mineral in the oxidized zone of arsenic-bearing lead deposits.
Mineral Association: Cerussite, anglesite, smithsonite, willemite, pyromorphite, wulfenite
  
Luminescent Properties: May fluoresce reddish yellow under LW or SW UV.
Other Properties: Piezoelectric. Gemstone Extremely Rare.

 

Mimetite
Bright orange fibrous mimetite to 6 mm and reddish wulfenite crystals to 1 cm
Origin: San Carlos, Chihuahua, Mexico
Sample size: 7 x 6 x 3 cm
Photo: Tom Loomis

 

Mimetite
(zoom-in of above)

 

Mimetite
Origin: near Huo Zhou City, Guangxi Province, China
Sample size: 8 x 6 x 3 cm
Photo: Rob Lavinsky

 

Mimetite
(zoom-in of above)

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