Back in 2007 when we began cataloguing Warren Taylor's Tsumeb minerals we came across a real stand out rock.
It was oddly labelled as "Quartz Psm Azurite" but was obviously gypsum and appeared to have formed around something round like a pipe.
Warren wasn't sure of its origin, though it was acquired with other minerals from Tsumeb and part of his collection.
Today, 10 years later Jill Brunner from Kalahari Minerals has been on to us about listing an oddball from Tsumeb; again not sure of how to classify it but she did have the story of the origin.
When I looked at the picture I immediately saw what it was and now of course have the back story for these bizarre blue-grey gypsum crystals.
The story (from Jill) - Known colloquially as a “backdoor” meaning that copper (and other minerals) were leaving the mine through the backdoor via the water pumping operation and that these would crystallise on the drainage pipes as water stilled on the surface.
Hence the large murky crystals with curvature to the back.
This is a phenomenon commonly seen in Australia, and of course the recent green colour specimens from Lubin in Poland; I hadn't heard of it before at Tsumeb.
When I visited Britannia Mine, in British Columbia, Canada you could see an elaborate array of boxes designed to slow the outflow down. These were filled with scrap iron to draw suspended copper from solution as the water pooled.
Glad we finally know the origin of Warren's cabinet oddity!
You can see Jill's specimen via the Item Link below.