Goethite

Goethite


Composition: FeO(OH)
Crystal System : Orthorhombic
Colours: Brownish-black, yellow-brown, reddish-brown
Lustre : Adamantine, metallic, silky, dull
Hardness (H) : 5.0-5.5
Specific Gravity (S.G) : 4.27-4.29
References: Keller (1977a)

Distribution

Very common. Present in all three oxidation zones.

Occurrence

  • Supergene
  • 1st Oxidation Zone
  • 2nd Oxidation Zone
  • 3rd Oxidation Zone

Notable Finds

As botryoidal masses in the third oxidation zone, on 46 Level (Gebhard, 1999).

Paragenetic and General Notes

Goethite is a common secondary mineral at Tsumeb.  It seldom forms attractive specimens in its own right, but occurs as an accessory constituent with a diverse range of mineral species and in various parageneses.

Keller (1977) noted that goethite tends to form early in the supergene process, and he included it in two of his "Type I" parageneses (i.e. associations forming under relatively high pH conditions):

(1)  Goethite >> duftite (I) >> cerussite >> duftite (II) >> dolomite

(2)  Goethite >> wulfenite >> mimetite >> malachite

Goethite is reported to form pseudomorphs after the following minerals: schultenite (rare).