Mineral - Magnetite
Magnetite
Chemical Properties
Mineral Class
Oxides and Hydrxides
Toxicity
none
Formula
Fe²⁺(Fe³⁺)₂O₄
Unit Cell
a=8.40 Z=8
Physical Properties
Hardness
5.5 - 6.5
Streak
black
Density
Heavy (3,5-6)
Cleavage
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
blackgray
Birefringence
Luster
Metallic
Transparency
opaque
Pleochroism
Geomineralogical Properties
Crystal System
isometric
Point Group
hexoctahedral - 4/m 3 2/m
Space Group
Fd 3 m (227)
Habit
coarse, dodecahedron, Octahedron, Cube
Formation
(1) Magmatic, through early crystalline precipitation and gravitational segregation from mafic to ultramafic melts or as an accessory in intermediate magmatites.
(2) Contact and regional metamorphic, in particular through the decarbonatization of iron-rich sediments or in the course of skarn formation.
(3) Hydrothermal, through precipitation from hot, mineralized solutions in veins or as metasomatic displacement.
Paragenesis
Twinning
Contact twins after {111} - Spinel law
Rarity
Common
Synonyms
Magnetite
Composition
Elements
Mass
SiO₂
0.27
Al₂O₃
0.21
Fe₂O₃
68.85
FeO
30.78
New York (Palache et al. 1952)
Groups and Members
Spinel-Supergroup
Oxyspinel-Group
Spinel-Subgroup