Geology weekend (1). 15- 17 June 2018.

What an absolute privilege and pleasure it was to be able to attend the lectures by Professor Judith Kinnaird, of The Geosciences School at Wits University this past weekend in the Borakalalo National Park boardroom. Such a stimulating and interesting presentation inspired us all to participate with avid attention. In addition, a large practical component was included which required some chemical and physical testing of the various minerals.

We were quickly corrected when calling these bricks ‘Rocks’, that they were in fact Minerals, and these large trays provided us with a considerable challenge to map our way around and understand this new topic.

‘Acid tests’ and ‘Hardness tests’ and terms such as ‘specific gravity’ required our full concentration. Testing the strength of the various minerals using our fingernails, a coin and then a small knife showed us the various properties of the different minerals.

Soon we were bandying terms around such as cleavage and fracture and looking at the amazingly beautiful colours of Malachite, Sulphur and Azurite. This cleavage is, of course, quite a different sort to what you are imagining.

Annette quietly asked which container had the diamonds; but unfortunately we were advised that there weren’t any diamonds available as samples!!

Talking about diamonds, we were told the fascinating tale of the Cullinan Diamond, which is the largest gem-quality rough diamond ever found, weighing 3,106.75 carats, discovered in 1905. Due to its immense value, detectives were assigned to a steamboat that was rumoured to be carrying the stone, and a parcel was ceremoniously locked in the captain’s safe and guarded for the entire journey. It was a diversionary tactic – the stone on that ship was fake, meant to attract those who would be interested in stealing it. The original was actually sent to the United Kingdom in a plain box via registered post!

Fig 1: Minerals.

It was truly incredible to discover that the Universe is 15 to 20 billion years old, and to think our own little contributions pass by in just 70 or more so years!! Quite sobering.


 Fig 2: Igneous Rocks.

Then finally onto Rocks. Igneous, metamorphic and sedimentary and the many rock types found in the Pilanesberg and Borakalalo.

We were told about the fascinating volcanic past of the Pilanesberg and the fact that the rocks there exclude granite but the common rocks there are syenite (in large quantities), which are similar to granite in composition, but lacking quartz. Wow!

A visit to the quarry at Borakalalo in the afternoon was a pleasant interlude, outdoors in the warm winter sunshine Ah!.

Fig 3: Prof Kinnaird continued her lectures outdoors in the quarry at Borakalolo.

The quarry is made from quartzite, metamorphised from sandstone laid down earlier. The layers which had been deposited could clearly be seen.  We were shown the strike and angle of the rock which is used on the maps to see how the rock has moved. We were also shown some cross-bedding where the lines of the sediment were aligned slightly differently- to the rest of the rock. We kept an eye out for any stray precious minerals which would have represented some modified quartz! There was another interesting rock that showed “Ripples” which was once the floor. It was amazing to think that we could tell the direction of the movement of water – by looking at which way the ripple leans.

We then headed to a small mountain on the other side of the dam wall, where we had a gentle climb up a slope to examine some igneous rocks. This clearly revealed a distinctive grain which allowed us to identify it as ‘igneous rock’. We were shown that we were near the crown of the upthrust, by small pockets of gas that formed little indentations in the rock. In addition, the difference between sedimentary rock and the cooling lines in this rock was explained. We were also shown a vertical fault line, and told that the river runs along another fault line, and that is why it is so straight and not curving.

A small mention has to be made of the extremely challenging test written on Friday on the topic: ‘Veld Management’, which required us all to become fire experts and soil scientists!

 Fig 4: Camp Fire Tales.

On Sunday, after the lecture, we took a long drive and walked up another slope. We did a soil test to see what type of soil was found in this slope. The soil on the top of the hill was very shallow and sandy, and there were a lot of rocks around. We then went to a lower point and the soil here was much deeper and had a higher clay content, with no rocks around. This most interestingly confirms the exact pattern of a typical Catena. There was also a very distinct line along the ridge, called a seep-line, where the vegetation changed dramatically.

The evening proved to be chilly, but nothing could dampen the warm enthusiasm of the vibrant and fascinating day. An absolutely wonderful weekend.

Ed’s Note: Many thanks to Sharon and the wetlands team for putting this detailed (and technical)  report together at such short notice.

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