Goethite

The most common simple iron oxide mineral. A weathering product of numerous iron-bearing minerals. Goethite may crystallize from a precursor - a not approved species called 'proto-goethite'. May also form due to mineralization of lichen (Parmelia conspersa) thalli on metamorphics (e.g., gneisses), granites, feldspars. Sulfidation of goethite into mackinawite and pyrrhotite is described by Wang et al. (2015); the process is inactive in the CH4 atmosphere but is triggered by the addition of CO2.

History

Activities related to discovery and approval of the group members

Structural context

Goethite
Crystal System orthorhombicSpace Group Pnma
a4.4683—9.9613 (5.0343)
b3.0128—10.0097 (9.3945)
c2.9739—4.6017 (3.1485)
alpha90
beta90
gamma90
volume130.669—140.6 (138.3856)

Based on 37 measurements

Chemical context

Stoichiometric formulas

Goethite
mindat.org
  • Feb. 23, 2025Fe3+O(OH)Previously \alpha-Fe#3+#O(OH)
  • March 13, 2023α-Fe3+O(OH)
IMA
  • March 13, 2023FeO(OH)
mineralogy.rocks
  • Aug. 30, 2022Fe3+O(OH)

Elements recorded on EPMA

36
Fe
36
O
31
H
4
Co

Physical properties

ColorColor entities, recognized using a custom trained NER model
  • brownish black
  • yellow-brown
  • reddish brown
Color noteOriginal color note from the source
Brownish black, yellow-brown, reddish brown
StreakStreak entities, recognized using a custom trained NER model
  • yellowish brown
  • orange-yellow
  • ocher-yellow
Streak noteOriginal streak note from the source
Yellowish brown, orange-yellow, ocher-yellow
Lustre
Adamantine
Silky
Metallic
Dull
Fracture
Irregular/Uneven
Transparency
Opaque
Tenacity
brittle
Hardness
5—5.5
Measured density
4.27—4.29
Calculated density
4.18