Mineral - Aenigmatite
Aenigmatite
Chemical Properties
Mineral Class
Silicates
Toxicity
none
Formula
Na₂Fe₅Ti[O₂|Si₆O₁₈]
Unit Cell
a=10.41 b=10.81 c=8.93 α=105° β=97° γ=125° Z=2
Physical Properties
Hardness
5.5 - 6
Streak
brownredred brown
Density
Heavy (3,5-6)
Cleavage
good after {010}, {100}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
blackbrown
Birefringence
0.100
Luster
Vitreous,
Greasy
Transparency
translucent,
opaque
Pleochroism
Geomineralogical Properties
Crystal System
triclinic
Point Group
triclinic-pinacoidal - 1
Space Group
P 1 (2)
Habit
prismatic
Formation
Under highly peralkaline, Si-undersaturated and Na-Fe-rich magmatic conditions in differentiated nepheline syenites, phonolitic lavas and pegmatitic rocks at high temperatures (>800 °C) and low oxygen fugacities
Paragenesis
Twinning
Rotation twins perpendicular to {011}
Rarity
Rarely
Synonyms
Aenigmatite
Composition
Elements
Mass
SiO₂
39.62
TiO₂
9.66
Al₂O₃
0.64
Fe₂O₃
4.64
FeO
33.92
MnO
2.46
MgO
1.65
CaO
0.44
Na₂O
7.20
K₂O
0.04
Cl
0.02
H₂O
0.05
Russia (Dana 1892)
Groups and Members
Sapphirine-Supergroup
Aenigmatite-Group
Name and first discovery : Named after the Greek word "aenigma" (riddle), alluding to its initially unknown chemical composition, aenigmatite and its type locality, the Ilimaussaq Intrusion in Greenland, were first described by August Breithaupt in 1865.
Chemistry :
Synonyms : Cossyrite, Cosyrite, Kölbingite
Varieties :
Abbreviation: Aen
literature
Dana, J. D., & Dana, E. S. (1892). The system of mineralogy of James Dwight Dana, 1837-1868: descriptive mineralogy . J. Wiley & sons.