Altenberg is a nice town located in the Ore Mountains about 30 km from Dresden and close to the border with Czech Republic. The town is a popular health resort in the region, also well known nowadays for hosting different sport championships such as the FIBT Worl Championship in 2008 (bobsleigh and tobogganing). People from Dresden and surrounding go often to Altenberg on short weekend walk outs and that’s what we also did recently on one of the few sunny winter days.

On our tour we got to walk around the two water bodies Western of Altenberg: Großer Galgenteich and Kleiner Galgenteich (Big and Small Galgen ponds). Both of them were previously used in the exploatation of Tin (the element described with chemical symbol Sn) but lost their original use due to ceasing of all mining activities in the region. Today the bigger one is used as drinking water reservoir and the small pond for recreational purposes. This includes also the 30 ml sand sample for our World Atlas of Sands collection (sample no 1406).

Last weekend we resumed our photography trials and got new results. The setup was slightly different because we have already been using the new Canon camera body. The lens was the same (EF 100 mm f/2.8 USM Macro) but coupled with a closeup adaptor (Marumi Achromat Macro 200). Since we used all the 21 MP of the new Canon sensor and the aperture stopped at f/16, the images came out crisp sharp even when using high magnification factors.

Starting with today we are the happy owners of a new photo camera: Canon 5D MK II. This was our dream since a while ago due to mainly two reasons: full format sensor and its amazing 21 MP resolution. I do not intend to write a full review here, my intention was only to share with you our happiness. I expect more sand photos to come in the near future so stay tuned and visit the Sand Atlas more often

Last year in September we spent an extended weekend on the Usedom island at the Baltic Sea  in NE Germany. We couldn’t go bathing but we had plenty of fun exploring the island and discovering its hidden misteries: the Butterfly Farm, the old Russian submarine at Peenemünde (a former Army Research Center during the World War II), the up-side-down house (the entire house is build and fully equipped with the up-side-down), trekking along the former German – Polish border (a sand stripe heavily mined before the Schengen agreement came into power eliminating the border formalities) and of course the delicious smoked fish along the beach.

Talking about beach… I definitely couldn’t just pass by without loading up a full bunch of 30 ml units, samples sorted out and added later to my Sand Atlas: light and fine, a classical “must have” bunch of beach sands (about 20 samples, most of them also available for trading).

Serpentine is a rock forming mineral found in many metamorphic and igneous rocks with chemical formula (Mg,Fe)3Si2O5(OH)4 and chemical name Magnesium Iron Silicate Hydroxide. The colour is mostly green and the crystals are translucent. In my Sand Atlas collection I have one sand with serpentine (no. 278) originating from Marine d’Albo on Corsica island in France (Ligurian Sea).

The sample (832) comes from the beach at Ustka, a Polish holiday resort at Baltic Sea. Probable composition: quartz, garnet and ilmenite, as Polish shorelines of Baltic Sea are known for deposits of sand enriched with heavy minerals such as zircon, garnet, magnetite, ilmenite, rutile, monazite.

Magnetite is a ferrimagnetic mineral known under the chemical name ferrous-feric oxide, having chemical formula Fe₃O₄. Magnetite is the most magnetic naturally occurring mineral on Earth being known since the ancient times. Magnetite is often found in beach sands with igneous and metamorphic origins.

The sample above comes from Bali island, Indonesia (sample no. 1005 in my Sand Atlas). When taking the photo I noticed some yellow-brown-kaki translucent grains (they were not visible with naked eye). I was just curious to know whether I can somehow sort out the “foreign” grains (presumably olivine).

Using a magnet the result was great: indeed, only some of the particles (about 2/3 from total volume) have been attracted by the magnet, the rest remaining still. I also noticed that not all dark particles were gone, some were ignoring the magnetic force, so that not everything was magnetite.

Sand grains occurr in different shapes and sizes according to mineral composition, age, transport mechanism and distance traveled. Old sands usually have a round shape due to repeated wheatering and action of external factors. If they are exposed to strong wind or tidal action, the roundness of the grains are more accentuated as for the more “static” sands. On opposite, younger sands produced artificially by crushing sandstone tend to be more irregular in shape, with “sharp” edges. Along a river, bigger (and heavier) particles are deposided upstream and the lighter grains are being carried away a longer distance and thus more prone to accentuated roundness.

Two geometrical parameters are used to describe the shape of sand grains, namely roundness and sfericity. Roundness is the measure describing the sharpness of a grain’s corners and edges, regardless of shape. A rather exact description of particle roundness has been proposed in 1932 by a scientist called Wadell as “the ratio of the average radius of curvature of the several edges or corners of the particle to the radius of curvature of the maximum inscribed sphere”. A perfect rounded particle would have the roundness = 1, all the others being included in different roundness classes (see also image below): well rounded (roundness value between 0.60 – 1.00), rounded (0.40 – 0.60), subrounded (0.25 – 0.40), subangular (0.15 – 0.25), angular (0.00 – 0.15), and very angular (class reserved for grains with extremely sharp edges).

Modified after Powers, M . C., 1953, Journal of Sedimentary Petrology, v. 23, p. 118

Sphericity is a measure of the degree to which the shape of a particle approaches that of a sphere. A perfect spherical grain would have the sfericity factor = 1 but this is rather uncommon in nature as most sand grains have sphericity numbers around 0.7 (in the image above, grains on the top line would have high sphericity values and those at the bottom low values).

Although elaborated methods have been developed for exact measuring the both parameters (e.g. by surface area measurement using laser scanner or using shape analysis sofware like ArcInfo), in practice more easier visual methods are used, such as Krumbein roundness chart and Riley sphericity index. For a better exemplification I inserted two images depicting quartz sands with different grain roundness and sphericity(left: subangular grains, right: rounded grains):

More info on roundness and sphericity:

• Krumbein, W. C. and L. L. Sloss (1951) Stratigraphy and Sedimentation. 2^nd. Ed. W. H. Freeman and Company. London
• Vepraskas, M. J. and Cassel, D. K. (1987) Sphericity and Roundness of Sand in Coastal Soils and Relationships with Soil Physical Properties. Soil Sci. Soc. Am. J. 51:1108-1112

Over the last weekend we had our first try in sand microphotography. Since we don’t have (yet!) a microscope we had to use our our digital camera. To get as much sharpness as possible we decided to mount a fix micro lens (Canon EF 100 mm f/2.8 USM) on the Canon 350D SLR body. Additional sharpness was provided by a small aperture (around F22) and a bit longer exposure times, as well as by using the camera’s self-timer and a tripod in order to avoid any hand shaking:

280 NL-NH, Netherlands, Wijk aan Zee, Floodline of beach, GPS 52°29′36″N 4°35′5″E (sea shells beach)

The results were astonishing taking into consideration the simple setup without any professional ligthining (we used only two regular 5 euro desk lights at an horizontal angle of about 15-30° for an increased 3D effect). We are looking so forward to the next photo session…!!!