Ancient Linden Greenstone EarthCache
Ancient Linden Greenstone
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Emma Park commemorates the centenary of the Groot Trek (where Afrikaner farmers moved from the Cape into the Free State & Transvaal). A number of vagrants have frequented this park in the past, so chose your time to go there accordingly.
Linden is a suburb that originated on the farm of Louw Geldenhuys (his house is a national monument in Emmarentia and he is buried there too). Apart from being a fairly old suburb, the rocks in this area are particularly old and interesting too. If it is safe - look at the monument on top of the hill too.
This outcrop (or koppie) is made up of among the oldest rocks found on earth. They were formed some 3500 million years ago. Collectively these rocks are often referred to as Greenstones. Although they resemble many other rocks and have a brownish colour, the name is derived from early field geologists who named rocks with a high percentage of “greenish” minerals greenstones. The minerals in question include: serpentine, chlorite, amphibole and fuchsite. These are characteristic minerals in mafic or ultramafic (i.e. non-acidic) rocks. These minerals are commonly found in rocks of this age across the globe, and are remnants of the earliest parts of the earth’s crust. These particular rocks are termed komatiites and are rich in the chemical magnesium. The name Komatiite is derived from the Komati River valley near Barberton in Mpumalanga where large belts of these greenstones are present. They were formed when hot magnesium rich magmas burst onto the surface of the earth’s early crust and cooled into these rocks. Being so ancient (often termed Archaean formations), the vast majority have been eroded or still lie covered. South Africa has an abundance of these rocks visible and geologists from across the world often travel to these sites to observe or collect samples.
The komatiitic volcanic rocks present in this area are about 2500 million years old and are among the oldest rocks on earth. This small hill (koppie) consists of serpentinite, a hydrated magnesium silicate rock that resulted from the alteration of the original peridotite which was abundant in the mineral olivine.
(Acknowledgments: guidebook to Sites of Geological & Mining Interest on the Central Witwatersrand.; Geological Society of South Africa; 1986).
NOTE: Please be aware of dubious looking muggles - SAFETY FIRST.
In order to qualify to log this cache, you need to answer the following questions and email the cache owner. Any logs not accompanied by an email will be deleted.
1) Take a photo of you and your GPSr with the greenstone outcrop visible and include in your log. Choose a spot that was of particular interest to yourself (anywhere on the koppie). [Optional]
2) Describe what the rock looks like (including texture and colours). Why do you think that it is so rough and not smooth?
3) Apart from the Greenstone – did you notice any other rocks in this area? Make an attempt of identifying or describing them in your post. Include how you think they may have gotten here (especially if you have already done a few other of the Earthcaches in the area – it may give some clues).
Additional Hints
(Decrypt)
Erzrzore gb fraq lbhe rznvy!