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.

Three photos from Vargyas Valley, Transylvania

A few weeks ago I have spent some time back home in Transylvania (it is actually a place previously known as home), and took a day to visit a special place, the ‘canyon’ of the Vargyas River; we used to do a lot of caving and hiking here when I was in high school. A small patch of Mesozoic limestones was somehow forgotten in the middle of a lot of softer pyroclastic deposits, and a nice little canyon developed, with lots of caves and typical karst morphology. Make no mistake, this is not a ‘grand’ canyon, it is not even among the largest canyons in Romania or Transylvania.

But often it is lesser known and more hidden places that have a special atmosphere, a special combination of colors, shapes, shades and minor details that you can never forget.

The Vargyas River

One of the caves

Chlorophyll rules at this time of the year

More pictures here. And here is a map:

Blast from the past: images from Peru

After several years of thinking and saying that I should do something about my old color slides that are only gathering dust in a corner, I finally did it: I sent a few hundred old pictures to Scancafe to have them scanned. It takes quite a bit of time to get the scans back, but it’s worth it. The quality is better than I expected, and even if I had somehow access to the right kind of scanner (the average scanner just won’t do it), I would have spent many hours doing this.

So I got the DVD today from Scancafe, and I keep looking at these pictures from Peru, taken during five weeks of field work in the Talara Basin, I think seven years ago, followed by a week of vacation in Cusco and Machu Picchu. They are either very good, or I had too much of a good time.

In either case, I’ve got to go back.

Peyto Lake / Caldron Lake trail

[This is my last post about Peyto Lake, I promise.]

Here is a KMZ (= Google Earth) file for the trail that leads from the Peyto Lake viewing platform to Caldron Lake. It corresponds to the red line in the screenshot below. It is obvious that we never got to Caldron Lake…

You can also see some of the photos in Google Earth, if you download and open this file.