A hidden gem which has had visitors for many many years – thanks to the natural geology of the area
The pass marks the boundary between Kwa Zulu Natal and the Free State provinces of South Africa. It is a famous pass that is closed from time to time when heavy snow falls block the road or serious traffic accidents occur on the road. It is also notorious for strong cross winds as you pass along the exposed ridges (but that is another topic entirely related to air pressure and wind formation due to the escarpment – aka known as “topographically induced winds” – check out MINZA and UMZANZI).
Ground Zero – or what are we looking for?
Within the matrix (surround rock that all looks the same) of the crumbly shales – you will observe some darker, rounder shaped rocks within the shale matrix. These are the subject of this Earthcache.
As you look around this slope (please be careful as it is very easy to slip on the steep slope and crumbly surface) – you should be able to see a good few of these “thingy-ma-bob” rocks within a 25 to 50 metre radius. Now here is the object of the Earthcache – what are they – and how were they likely to form?
Well I don’t know – that’s why I asked you to come and look J - …. Only joking!
In geological speak – these are known as either CONCRETIONS or NODULES. But what is the difference?
Concretion or Nodule?
Concretions: These are aggregates that occur within sedimentary rocks (like shales and sandstones – spot the clue) and are composed of inorganic material (i.e. they are also “rocks” or minerals). They are often spheroidal or discoidal (disc like) in shape. Generally (but not always) they are composed of a single mineral – so are often uniform in structure and colour (except for exposed and weathered pieces) – impurities can make colour differences – but these are often seen in a layer or band within the concretion. Sometimes concretions will form around a foreign object in the original sediments. So it is not uncommon to “break open” a concretion and find a fossil inside. They are not fossils themselves – but may contain fossils – and are often used as indicators for fossil hunters in areas that are rich in fossils. So nodules mostly form around an object (it may be a pebble, a leaf or a bone) – or a gap/hole that exists in the sediment.
Nodules: Nodules appear very similar to concretions, and the terms are often used interchangeably. They differ in that they are not formed around something – but are a “replacement” of a mineral within the rock matrix. So what one sees is a very different mineral from the surrounding rock (e.g. a manganese or pyrite nodule within a siltstone or coal). Nodules are also often associated with metamorphosed rocks too.
Your tasks – the C.S.I. work!
In order to substantiate your visit and be able to claim this Earthcache, a number of questions need to be answered and submitted to the cache developer, via e-mail.
1 – Look around the site and find a few of these geological “oddities” so that you can analyse them. Look at the shape, colour, way that they have weathered and type of material that makes up these inclusions. Describe them.
2 – Based on your answers in “1” above – do you think these are CONCRETIONS or NODULES? Why do you say this?
3 – Describe any other interesting things you saw or experiences you had on site (you can add these to your log too for others to enjoy too). Photos are always welcomed in the logs.
NOTE: You may log your visit prior to approval, but e-mail submissions that do not meet the above criteria will be deleted.
