The history:
South African chromite resources of the Bushveld Complex are enormous and account for 54% of the world's chrome ore reserves. The chrome seams are distributed over a stratigraghic thickness of 300 to 1000m and are associated with a number of rocks that vary from peridotite to anorthosite. The thickness of the seams varies from a few centimeters to 1.8m. More than 15 sizeable seams may be present in a single section ans some may be traced over distances of more than 200km.1
Minerals:
Although the chrome mines of South Africa are not known for aesthetic mineral their zeolites and calcites are notable exceptions. The Mooinooi Chrome Mine in the Rustenburg district containes small pocketsand veins of white to cream coloured stilbite crystals displaying a typical pearl lustre. These crystals were small and reached a maximum dimension of 2cm. What made these specimens interesting was also that the matrix of some consisted of black, granular chromite crystals - an unusual association. Pearly-white, coffin-shaped heulandite crystal aggregates of up to 2cm are very occasionally found on the stilbite groups. Fine, delicate sprays of natrolite were also found [view image below] as well as more robust individual crystals, 3cm long by 3mm wide.2
[close up]
Microscopic laumontite crystals and amber euhedral calcite up to 4cm on edge as seen on the image below also occur in association. Furthermore pseudo-cubic pale green semi-transparent flourapophyllite crystals, either single crystals up to 2cm. or aggregate groups made up of several individuals have also been found. Another occurance has been doubly terminated white to semi-transparent scalenohedral calcite "floates" up to 7cm as well as yellow flouresent orange calcite crytals up to 5cm. The latter type of calcite occured manly on breccia covered with laumontite. Very dark brown dravite tourmaline (up to 2cm) was also encountered in assocition with a fault zone.3
A handful of extremely aesthetic natrolite specimens were found at Chrome Mine (potgietersrus district) in the 1970s [as seen below]. These consist of snow white sprays up to 4cm diameter, each composed of many euhedral crystals up to 4cm long, perched on a black chromite strata.4
The Montrose Chrome Mine in the Steelpoort sistrict produced some interesting specimens of aragonitic dipstone. These were cream coloured to chocolate brown slabs of highly botryoidal to reniform masses of aragonite. This aragonite was usually found on chromite.5
Buying/collecting:
The minerals from the chrome mines come from local geologists.
Footnotes
"Minerals of South Africa" by Bruce Cairncross and Roger Dixon:
1: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 91f.
2: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 92 and 244.
3: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 92.
4: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 92f.
5: Cairncross, B./Dixon, R.: in Minerals of South Africa, Singapore 1995, p. 111.
Back to Home
