Siderite

Siderite


Composition: FeCO3
Crystal System : Cubic; Hexagonal
Colours: Yellow-brown, sherry-brown, beige, tan, greenish-yellow
Lustre : Vitreous, dull
Hardness (H) : 4
Specific Gravity (S.G) : 3.96
References: Gebhard (1999)

Distribution

Common. Present in all three oxidation zones.

Occurrence

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

Paragenetic and General Notes

Although siderite is common at Tsumeb, specimen-quality material is rare.  Three occurrences of siderite stand out: 

(1) Gemmy, yellow, or red-brown scalenohedra and modified rhombohedral crystals, to about 10 mm, on a matrix of massive chalcocite / tennantite ore, from the second oxidation zone.

(2) Brown, or beige-coloured crystals in vugs in germanium-rich sulphide ores accompanying minerals such as ludlockite and stottite, and sometimes resembling the latter. Siderite in this paragenesis typically contains up to 9% zinc and is commonly referred to as zincian siderite. 

(3) In the third oxidation zone, on 46 Level, greenish-disc-like crystals of siderite are associated with chalcocite, and samples of this siderite may contains up to 8.5% nickel (Gebhard, 1999).