Mineral - Goethite
Goethite
Chemical Properties
Mineral Class
Oxides and Hydrxides
Toxicity
none
Formula
Fe³⁺O(OH)
Unit Cell
a=4.61 b=9.96 c=3.02 Z=4
Physical Properties
Hardness
5 - 5.5
Streak
brownyellowyellow brown
Density
Heavy (3,5-6)
Cleavage
Perfect after {010}
Fracture
uneven
Tenacity
Brittle
Optical Properties
Color
brownyellow
Birefringence
0.134
Luster
Metallic,
Silky,
Adamantine
Transparency
opaque
Pleochroism
Gelb/Braun
Geomineralogical Properties
Crystal System
orthorhombic
Point Group
orthorhombic-dipyramidal - 2/m 2/m 2/m
Space Group
Pnma (62)
Habit
dendritic, coarse, bulbous, crusty, massive, acicular, kidney-shaped, prismatic, radial, stalactitic, radial, grape-shaped
Formation
Oxidation zone of iron deposits
Paragenesis
Twinning
Rarity
Very common
Synonyms
Goethite
Composition
Elements
Mass
SiO₂
0.36
Fe₂O₃
89.65
H₂O
10.19
Colorado (Palache et al. 1952)
Groups and Members
Diaspore-Group