Sunday, November 30, 2008

Images from South Africa: Patterns

A few more photos from the same trip that I already posted photographic highlights from. To be more factual and fair, the title should be "Images from the Western Cape", because I have only seen a few places in South Africa, and all of those places are in the Western Cape province. Anyway, here are three photos of... well, not much, just some visually interesting patterns.

Halophytic (salt-loving) vegetation in the supratidal zone of the Langebaan Lagoon, West Coast National Park

Old tree trunk at Groot Constantia winery, Cape Town, the first winery in South Africa, created in 1685

A look at the pebble (beach near Cape of Good Hope)

Friday, November 21, 2008

Liesegang bands in sandstone

Liesegang bands are poorly understood chemical structures often seen in rocks, especially sandstones. They were discovered more than a hundred years ago by the German chemist Raphael E. Liesegang, when he accidentally dropped a drop of silver nitrate solution on a layer of gel containing potassium dichromate, and concentric rings of silver dichromate started to form.

In sedimentary rocks, Liesegang bands appear well after the sediment has become a rock (that is, it got compacted and cemented). Stratification and lamination within the sansdtone are typically cross-cut by the Liesegang bands; fractures usually have a more obvious effect on the distribution and orientation of these.

The rocks shown here are turbidites of the Permian Skoorstenberg Formation, in the Karoo desert of South Africa. This Liesegang banding developed in the neighborhood of a small thrust and consists of brown bands of iron oxide that entirely 'ignore' the original lamination of the sandstone (not visible in the photos), but clearly like to precipitate along some of the fractures in the rock.

Sunday, November 02, 2008

Images from South Africa: Landscapes

Follow-up from previous post: three landscape photographs, hot off the memory card, uploaded from a hotel room in Cape Town.

Karoo landscape

Table Mountain landscape

Cape Town landscape

In case you want to see more, the rest of the pics are here.

Images from South Africa: Flowers

I have spent some time in South Africa, mostly looking at turbidites of the Tanqua Karoo. One of course cannot refrain from looking at other things as well, apart from turbidites, so here is a taste of how the Karoo looks like after an unusually wet winter. Apparently there haven't been this many flowers in the last 40 years or so. The rest of the photos are here.

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