Mineral - Allactite
Allactite
Chemical Properties
Mineral Class
Arsenates
Toxicity
low
Formula
Mn²⁺₇(AsO₄)₂(OH)₈
Unit Cell
a=11.03 b=12.12 c=5.51 β=114° Z=2
Physical Properties
Hardness
4.5
Streak
browngraygray brown
Density
Heavy (3,5-6)
Cleavage
Indistinct after {001}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
brownredorangepinkcolorless
Birefringence
0.019 - 0.026
Luster
Vitreous,
Greasy
Transparency
translucent,
transparent
Pleochroism
Geomineralogical Properties
Crystal System
monoclinic
Point Group
monoclinic-prismatic - 2/m
Space Group
P2 1 /c (14)
Habit
leafy, rosette, tabular
Formation
Metamorphism and metasomatism of manganese or/and zinc ore bodies
Paragenesis
Twinning
Rarity
Very rare
Synonyms
Allactite
Composition
Elements
Mass
As₂O₅
25.40
FeO
0.40
MnO
62.00
ZnO
2.30
MgO
0.20
CaO
0.60
H₂O
9.00
New Jersey (Moore 1968)
Groups and Members
Allactite-Group
Name and first discovery : Named after the Greek word for "change" (allaktein), due to its intense pleochroism. Discovered in Sweden in 1884.
Chemistry :
Synonyms : Elfstorpit
Varieties :
Abbreviation : Ala
literature
Moore, P.B. (1968). Crystal chemistry of the basic manganese arsenate minerals: II. The crystal structure of allactite. American Mineralogist: Journal of Earth and Planetary Materials , 53 (5-6), 733-741.