Microscopy of sand

Sand can look beautiful under the microscope. Of course there are many different types of sand and so far I have only studied a few types with the microscope. When someone I know goes on a distant vacation, I usually ask to bring back some sand. The colours of sand grains indicate which minerals they contain. Red sand grains, for example, derive their color from the presence of iron-containing minerals. The purer the sand, the whiter. White sand consists largely of quartz (silicon dioxide, SiO2) and the less contaminants it contains, the whiter it will be. The mineral olivine is a silicate containing magnesium and iron, (Mg, Fe) 2SiO4, and its presence causes a green color in sand grains. On islands with a volcanic past you can find black sand on the beach and this sand consists largely of basalt, which was formed by the rapid solidification of lava. I have only just started doing microphotography of sand and some images are shown in this article.

Red sand from the Outback in Australia fotographed in darkfield illumination. Objective: Olympus 10/0.25 (37 mm).

Also from Australia: sand as white as sugar and of a high purity. This sand consists almost entirely of quartz. Photographed with incident light. Objective: Leitz 4/0.12.

Sand from a beach at South Coast of England fotographed in brightfield illumination. Objective: Carl Zeiss 3.2/0.07.

Sand from the Kennemerduinen, locationt Wed. Fotographed with a combination of brightfield illumination and incident light. Objective: Leitz 4/0.12.

Sand from 'Berg en Dal', Suriname. Fotographed with a combination of brightfield illumination and incident light. Objective: Carl Zeiss Neofluar 6.3/0.20

Sand from location Vossenberg’, Meijel (Limburg). Fotographed with incident light. Objective: Leitz 4/0.12.

Sand from a beach at Texel, location 'Mok'. Fotographed with darkfield illumination. Objective: Carl Zeiss Neofluar 6.3/0.20.

Sand from a beach at IJmuiden photographed in brightfield (left, Carl Zeiss 3.2/0.07) and darkfield (right, Zeiss Neofluar 10/0.30).

Sand from a construction site at a road fotographed with incident light. Objective: Carl Zeiss Neofluar 6.3/0.20.

Sand from Kijkduin fotographed with a combination of darkfield illumination and incident light. Objective: Carl Zeiss Neofluar 6.3/0.20.

Technique

I experimented a bit with different illumination techniques. I noticed that some combinations of different illumination techniques can give interesting results. The colors in sand grains, for example, become more visible with darkfield illumination or with incident light at an angle. For incident light, I usually use a Jansjö LED lamp (IKEA) where I apply a diffuser or a piece of paper to get a more diffused light. This reduces disturbing light reflections. I always suspend the sand grains in a drop of water, which makes them more transparent.

The effect of different lighting techniques becomes clear in the following images. Here I illuminated the sand in different ways and I also tested combinations of different illumination techniques. I also looked at the effect of the color temperature of the light source. The Jansjö LED lamp normally gives a yellowish light that can be corrected with a blue filter to create white light. However, with a higher color temperature, the sand grains appeared to have less pronounced colors.

Sand from the Kennemerduinen photographed with Leitz 4/0.12 and illuminated in different ways. Upper 3 images, from left to right:

1. darkfield illumination,

2. brightfield illumination

3. oblique illumination.

Lower 3 images, from left to right:

4. Jansjö with blue filter, illumination from 1 site

5. Jansjö with blue filter, illumination from 1 site combined with brightfield illumination

6. Jansjö without blue filter, illumination from 1 site combined with brightfield illumination

It is striking that transparent sand grains with the combination of bright field illumination and illumination from one side appear very dark, as if they are black (images 5 and 6). This, of course, does not correspond to reality. Actual color differences are better represented with pure incident light (illumination from 1 side), brightfield and darkfield illumination.