Visit to Mineral Services and the Exhibition “Messengers From The Mantle”

March 29, 2018


By kind invitation of Professor John Gurney, 25 club members visited Mineral Services on 24th February to see his exceptional exhibition “Messengers from the Mantle”. This irreplaceable collection of kimberlites was initially created for the 35th International Geological Congress at the Cape Town International Convention Centre in September 2016, and was displayed again at the 11th International Kimberlite Conference in Gaborone, Botswana in September 2017. http://www.messengersfromthemantle.co.za/

Kimberlite rocks https://en.wikipedia.org/wiki/kimberlite are known for bringing up diamonds from deep in the mantle to the surface of the Earth, but they also provide scientists with important clues to the composition of rocks deep in the Earth below the lithosphere. Rocks from the Mantle Room collection at the University of Cape Town were selected for this exhibition, and many were sawn into very thin slices by our own Henri Schram. After sawing, the slabs were glued onto glass, polished even finer, mounted in display stands of lazer-cut steel echoing the shape of the section, and lit from behind. John Gurney and Phil Janney from UCT showed us around. Photos below show and describe a little of what we saw.

 
Dr Phil Janney explaining the contents of the showcases

 
John Gurney is seen here setting up the specimen shown on the right for us to look at. It shows evidence of having been a surface rock in its way distant past, which then was subducted back down into the mantle, only to return to the surface again in a kimberlite pipe bringing diamonds with it




The small photos are thin polished sections of different examples of kimberlite


Composition of kimberlite



 
John has also created a craft beer brewery and restaurant at the back of his premises. Some of our group moved on there after viewing the exhibition to taste the beer and chat further with John and Phil

Our special thanks go to John Gurney and Henri Schram for setting up this outing for us, and to Annette Schram for the following photos


Henri and John Gurney


Henri admiring some of his polished rock slices


Some of the ladies who attended

The library now has for loan a copy of the book “Barren Lands” by Kevin Krajick. This book details the hunt for diamonds in Canada, and the large part that John Gurney played in this.

“... the global intrigues and daunting natural forces facing protagonists Charles Fipke and Stewart Blusson as they race against the mighty DeBeers cartel in the 1990s, this is the definitive account of one of the world’s great mineral discoveries. It is also a tale of supreme adventure, taking the reader into a magical – and now fast-vanishing – wild landscape.”   First come, first served!

If you are interested in learning more about kimberlites and how they formed, see also

https://www.news.uct.ac.za/article/-2016-08-15-diamonds-a-scientists-best-friend

Or watch these short videos

https://ru-clip.com/video/1mowBvsTrBo/video-1-geophysics-12mbs.html

https://ru-clip.com/video/EAmab-UlQo4/video-2-kimberlites-12mbs.html

https://ru-clip.com/video/sO_Ndiw8fCY/video-3-peridotites-12mbs.html

https://ru-clip.com/video/Xv6E63YA7EA/video-4-eclogites2-12mbs.html

https://ru-clip.com/video/gFVLLS_jzGc/video-5-diamonds-and-metasomatism-12mbs.html

 


 

Field Trip to Yzerfontein

March 29, 2018
Sunday, 18th March

Pictures speak louder than words.


Brunsvigias alongside the West Coast road


24 members learning about an example of gabbro


Coastal erosion from the winter storms of 2017


An igneous breccia dyke


A 70,000 year old archaeological midden


Inspecting rocks on Schaapen Eiland


Iron pyrites


Inclusions of gabbro in the breccia dyke


Inclusions of chilled wall rock in the monzonite

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Faceting

January 17, 2018

 A magnificent 63 carat sphalerite from Aliva in Spain (http://gem-sphalerite.com/) cut by Duncan Miller. The design is Marco Voltolini’s “Superstarfish Dome 80”.

 

 A unique type of blue-green garnet has entered the gem market. The garnets reportedly come from a deposit near the border of Tanzania and Kenya. GIA’s Carlsbad laboratory obtained a small parcel of blue-green rough material and two faceted stones for examination. Unlike traditional blue-green garnets that exhibit a colo...


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“Tripping” in Namibia

November 24, 2017

The word “tripping” can have two meanings:  a tour or journey, or an unintentional slip, blunder or happening.  On this occasion both senses of the word applied. Malcolm and his friends covered a lot of ground and saw a wide variety of things when in Namibia, but not without incident.

To start off with, by the time Australian Graham landed in Cape Town, he had lost his passport, which necessitated a return to Johannesburg and the Australian Consulate for a new one. He then flew from JHB...


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Faceting

November 24, 2017

 

“Eye of the Storm” a faceting design created by Robert W. Strickland on 12th September 2017, in honour of those who suffered loss in the Caribbean hurricanes of 2017.

This design was first published in the United States Faceters’ Guild newsletter of September 2017.

When photographed directly into the centre of the culet, all the crown facets go dark, and the only light is in the “eye”, but viewed from other angles, the stone ...


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THE POLARISCOPE, THE FACETER’S FRIEND

September 23, 2017

Duncan Miller

A polariscope consists essentially of two polaroid filters, or a source of plane polarised light and one polaroid filter. The source of polarised light can be a white computer screen or even the sky, viewed at 90 degrees to the Sun. For the filter, or analyser, you can use a sheet of polaroid, or a lens from a cheap pair of 3D movie spectacles.

Let’s start with a white computer flat screen. Even an older cell phone screen without a plastic cover produces plane polarised ligh...


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9th September, 2017. The Jan Coetzee Quartz Crystal Reunion

September 23, 2017

About ten intrepid Jan Coetzee crystals made it to the reunion, with two of 50 kg-plus guys sending their apologies due to being overweight, along with a couple more whose owner couldn’t provide transport on the day. One rare and seldom seen fluorite (also from the same crystal pocket) came, and was much admired. Malcolm Jackson gave a short presentation about the mine and its location, along with photos taken by him and Jo of the Jan Coetzee mine dumps in recent years and the remains of th...


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FACETING THE NAMIBIAN RARITIES

August 24, 2017

Duncan Miller

During the 1974/75 university holidays I was fortunate to work for Sid Pieters in Windhoek for several months. It was a wonderful experience, including seeing some of the most famous mineral specimens then coming out of Tsumeb, but also to encounter some very special gem materials. Through Sid Pieters’s generosity I returned home to Cape Town with a few small fragments of jeremejevite from the original Namibian occurrence at Cape Cross and some pieces of cuprite from Onganja t...


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Curling Stones

August 24, 2017

Lesley Andrews gave a most interesting talk on Scottish curling stones. I thought curling was a Scottish winter game played by village yokels. I was wrong! It has had Winter Olympic status since 1998. The game consists of two teams of four players each, with eight stones between them, and the idea is to slide the stone, which turns, hence the name curling, towards a target called a button. Rather like a game of bowls on ice. The origin of the game goes back into obscurity, but the oldest know...


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FACETING FOR INCLUSIONS

July 24, 2017

Duncan Miller

Inclusions in gemstones often are seen as just a nuisance by faceters, who find themselves urged to buy only ‘clean’ rough. I suppose it is a matter of taste, but inclusions that do not detract from the visual appearance of a gemstone can aid in proving its authenticity. And some inclusions definitely enhance the value and appearance of certain gems. A visible ‘horse tail’ inclusion of asbestos fibres in Russian demantoid is perhaps the most famous example of desirable ...


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