09. The impact of Sodium Bicarbonate and the Twaing Impact Crater

The impact of Sodium Bicarbonate and the Twaing Impact Crater
By Eben van Tonder
26 June 2019



There are many ancient salts on earth. Over the years of studying many of them, I discovered a unique and fundamental property. They are alive, able to speak, reason and will!

They direct me in my everyday work at the deli meat producer in Johannesburg, Van Wyngaardt. They commune with me at night when I sleep. They do not let me rest, directing my thoughts and inquiries. The spirit of ammonia, spirit of saltpeter, spirit of sal ammoniac, spirit of soda ash, spirit of soda; these collectively form the Spiritus Mundi, literally, the World Spirit, which, in the interpretation of Yeates, contains the collective soul of the universe, the repository of the memories of all time.

Salt and the peoples of Southern Africa

Crosscurrents converged. For years I have been studying salt from the perspective of the people of Southern Africa. I took some time during two long visits to New Zealand to study the ancient salt production in that country and expanded it to Polynesia and touching on Taiwan and China to gain a better understanding of the regional technology related to salt. I became convinced that even if there was no actual salt production in pre-colonial New Zealand, that this does not mean that the Maori did not have a sophisticated knowledge of salt, as did the people from the region it finds itself in.

Back in South Africa, I fell in love with another great African technology of cattle breading when I was introduced to the subject of the Nguni by Etienne Lotter. It is the Nguni cattle which in turn lead me to the great indigenous cultures of sub-Sahara Africa and I started seeing these people, not as primitive humans, but very sophisticated societies.

I was trying to imagine apart from sodium chloride, what salts would the peoples of southern Africa have encountered and then, more importantly, what did they use it for. The most obvious answer for me, apart from sodium chloride, was to start with bicarbonate of either sodium of calcium.

Sodium Bicarbonate

Calcium bicarbonate was a logical starting point due to the existence of so many limestone caves in Southern Africa. My own exposure to caves taught me that stalactites and stalagmites form in limestone caves. Limestone contains at least 50% of calcium carbonate which dissolves in water. The water, in turn, contains carbon dioxide. Calcium bicarbonate is formed and the reaction is represented as follows:

calcium carbonate in water with carbon dioxide

The water with the calcium bicarbonate travels through the ground to the roof of the cavern where it comes into contact with air and a reaction takes place that creates calcium carbonate again which is deposited on the cave floor or suspended from the ceiling forming either stalagmites and stalactites. The reverse reaction where the calcium carbonate is created is represented as follows:

calcium bicarbonate to calcium carbonate.png

We are familiar with the effects of calcium bicarbonate in hard water where buildup is caused in one’s bathroom or kitchen and is difficult to clean. In limestone caves, the white calcium buildup is seen everywhere and these would have been tested by the industrious Africans. The custodians of chemical technology in Africa, as in probably all parts of the globe, was at some point the domain of the Sharma and healers. The white precipitate in the caves would have been heated, burned, rubbed onto wounds, tasted, used in foods, in water, in drinks and part of various potions and purely based on observation and by elimination, the properties of the salt would have been elucidated.

Calcium carbonate and calcium bicarbonate in terms of food preparations and preservation would not have done much. The only place on earth where I could find calcium carbonate or bicarbonate being used in food preparations is in Korea. Sodium bicarbonate, however, is a completely different story. I knew this from my work on another great African salt, Natron.


Natron contains around 17% sodium bicarbonate (NaHCO3). The other chemical present is sodium carbonate decahydrate (Na2CO3·10H2O, a kind of soda ash) and a small quantity of sodium chloride and sodium sulfate. I was first alerted to the preserving power of Natron when I realised its role in embalming. (Salt – 7000 years of meat curing) It is not hard to guess the extreme effective nature of sodium bicarbonate in preservation.

Corral, Laurie, Thomas, and Montville (1988) published a key paper on the use of sodium bicarbonate in meat preservation, Antimicrobial Activity of Sodium Bicarbonate.

I, myself, started using it with tremendous effect as a meat preservative. I wondered if there is any place in Southern Africa where sodium bicarbonate naturally occurs.


Twaing Impact Crater

Of course, it occurred naturally wherever Natron was found, but what about Southern Africa? To my great surprise, one of the very few places sodium bicarbonate naturally occurs is at a very special site, 40km’s North of Pretoria called Twaing. It means “the place where salt is.”

Around 220 000 there was an event where a meteorite struck the earth at this site. It exploded and vaporized on impact and the impact craters and the salt lake was formed.  The small groups started visiting Twaing between 130 000 and 30 000 years ago after the plant life was restored and animals returned to the region following the impact event. These groups came here to hunt, gather plant to eat and use for medicine and, of course, to collect salt. They made stone age tools and weapons. Scrapers, points and stone tools that were thrown away were found at Twaing. None of the rocks at Tswaing is suitable for making such tools and points, showing that these objects were brought from somewhere else. Interestingly enough, there were also artifacts found at Twaing that is smaller than the ones from the Middle Stone Age which we just referred to. This may indicate that the ancestors of the San Bushman who lived from 30 000 to 2000 years ago visited the site during a time known as the Late Stone Age.

The first ancestors of the current indigenous people, the first farmers to use iron age tools, migrated to South Africa 1850 years ago. The first Iron age people came to Twaing around 800 and 900 years ago. Decorated clay pot fragments found on the crater floor shows that these people were Sotho or Tswana speaking communities known as the Miloko who used the salt to preserve and flavour food and trade with it. It shows that by and large, people did not stay very long at Tswaing. It seems that most people who came to the crater was periodic visitors from the Waterberg area (and other locations). So far they have only found one Iron Age community at Tswaing along with a grindstone, decorated and undecorated potsherds.

There is evidence that the salt they collected was used for flavouring, food preservation, and trading. A large number of undecorated potsherds found in the crater indicate shows that Tswana and Sotho speaking people made up most of the visitors until the advent of the time of the Matabele in the 1820’s.

In the 19th century, factors such as drought, famine, competition for grazing, wood, and water and trading routes precipitated tremendous unrest and conflict between the Iron Age Inhabitants of South Africa. New political groupings were formed and new kingdoms emerged and militarism grew.

One such empire was the Ndebele (Matebele) empire. They established themselves north of the Vaal River in the early 1820’s. A band of Nguni refugees under Mziklikazi from KwaZulu-Natal started attacking and defeating Sotho tribes. In 1827, the kingdom relocated to the Magaliesburg region. From there they launched attacked and conquering Tswana/ Sotho chiefdoms to the North and West. It has not been proven, but it is very possible that the Matebele visited Twaing to collect salt and hunt the many wild animals who congregated there.

For most of the 19th Century, Tswaing remained the key salt lick north of Pretoria. Large herds of game gathered here including elephants until the early mechanized salt mining operation scared them away.

Tswaing: Sodium Bicarbonate and an Impact Crater – a massive impact

On Saturday, 22 June I visited the Tswaing impact crater and salt lake. I set off with a guide on the roughly 7km hike on the crater rim. In the first video, I arrive at the salt lake and impact crater.

Arriving at the water’s edge. The boreholes were drilled as a means to extract the salt brine. The taste of the salt is amazing! It has a depth in taste that surprises you! It is less salty than one expects and the aftertaste is exquisite!

Sampling the salt and the background of the salt.

What was it like arriving at the site 200 years ago?

Running towards the water’s edge.

Taking water samples and thinking about life.

Photos from the impact crater.


The impact of the crater has been profound. The knowledge of the ancients was impressive and their technology sophisticated. Sharing the space and knowledge possessed by the ancients is one of the highest privileges on earth! It was fantastic being here and continuing to understand the implications of this site.


All information about Twaing, from the official documentation and resources at the site.

Arnay-de-la-Rosa, M., González-Reimers, E., Pou-Hernández, S., Marrero-Salas, E., and García-Avila, C.. 2017. Prehispanic (Guanches) mummies and natrium salts in buria caves of Las Cañadas del Teide (Tenerife). E. Schweizerbart’sche Verlagsbuchhandlung, 70176 Stuttgart, Germany http://www.schweizerbart.de
DOI: 10.1127/anthranz/2017/0662.