Dolomite

Dolomite


Composition: CaMg(CO3)2
Crystal System : Trigonal
Colours: White, cream, pale-green, pale-pink, pink
Lustre : Vitreous, pearly
Hardness (H) : 3.5-4.0
Specific Gravity (S.G) : 2.84-2.86

Distribution

Abundant. Widespread throughout the Tsumeb deposit as a constituent of the host stratigraphy (dolostone), but also as well-formed crystals (and crystalline crusts) associated with both hypogene and supergene processes.

Occurrence

  • Hypogene
  • Supergene
  • Country Rock
  • 1st Oxidation Zone
  • 2nd Oxidation Zone
  • 3rd Oxidation Zone

Notable Finds

The epimorphic "casts" of dolomite, after calcite (and possibly other minerals) occur in both the first and second oxidation zones and make for unusual and attractive specimens.

Paragenetic and General Notes

Dolomite colour is strongly influenced by the presence of transition metals in solid solution. These include copper and zinc (with tendeny to cause green or bluish-green colouration); cobalt and manganese (with a tendency to cause various shades of pink).

Notably, Tsumeb dolomites containing nearly 5% zinc, and nearly 9% lead have been recorded (Hurlbut, 1957).

Dolomite is reported to form pseudomorphs after the following minerals:  azurite (rare, as epimorphs); calcite (common, often as epimorphs); cerussite (rare, as epimorphs); tennantite (common).

The following minerals are reported to form pseudomorphs after dolomite:  bayldonite (rare); duftite (rare).