Mineral Information and Data:

Allactite
Mn2+7(AsO4)2(OH)8 [CNMNC approved formula]

Named from the Greek, to change, a reference to the strong pleochroism.

IMA status : Valid species (Pre-IMA 1884) Grandfathered
CLASSIFICATION 
Dana
(8th edition) :
41.02.01.01  
  (41) Anhydrous Phosphates Containing Hydroxyl or Halogen
  (41.02) where (A B)7 (XO4)2 Zq
  (41.02.01) Allactite Group
  
Nickel-Strunz
(10th edition) :
08.BE.30
  (08) Phosphates, Arsenates, Vanadates
  (08.B) Phosphates, etc. with Additional Anions, without H2O
  (08.BE) With only medium-sized cations, (OH, etc.):RO4 > 2:1
  
Crystal system: Monoclinic System
Point group (H-M): 2/m — prismatic
Unit cell: a = 11.03 Å, b = 12.12 Å, c = 5.51 Å, b = 114.1°
Crystal Habit: Crystals slender prismatic or tabular; rosette-like aggregates
  
Color: Light to dark brownish red or purplish-red
Diaphaneity: Translucent
Luster: Vitreous, slightly greasy to oily on fresh fracture
Hardness (Mohs): 4.5
Measured Density: 3.83 g/cm3
Cleavage: 1; {001} distinct
Tenacity: Brittle
Fracture: Uneven
Streak: Grey to faint brown
  
Geologic Setting: As a rare secondary mineral in veinlets through metamorphosed manganese deposits (Sweden); in a metamorphosed stratiform zinc orebody (Franklin, New Jersey, USA).
Mineral Association: Synadelphite, hematolite, hausmannite, pyrochroite, fluorite (Moss mine, Sweden); pyroaurite, leucophoenicite, hodgkinsonite, adelite, franklinite, willemite, friedelite, caryopilite, sphalerite, fluorite, barite, calcite, serpentine, chlorite (Franklin, New Jersey, USA)
  
Other Properties: Gemstone Unlikely Available.

 

Allactite
Origin: Moss mine, Nordmark, Varmland, Sweden
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Allactite
Origin: Moss mine, Nordmark, Varmland, Sweden
Sample size: Microscopic image
Photo and Owner: Lou Perloff

 

Allactite
Specimen consists almost entirely of calcite. There are two exposed veins, however, which are lined with brownish colored crystals of allactite and colorless barite. The crystals of allactite are small but abundant where they are found on this specimen. The largest crystal is perhaps 1mm across at best.
Origin: Långban, Sweden
Sample size: 9.5 x 6.5 x 5.5 cm
Photo: John Veevaert, Trinity Mineral Co

 

Allactite
(zoom-in of above)

 

Allactite
(zoom-in of above)

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