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We don't have a sense of scale for the very small, and gigapan + microscopes (optical or SEM) can go a huge way towards opening the country of the very small to a wider public. Richard Feynman wrote There's plenty of room at the Bottom, but even if you have read that (more than once :-), you still don't get the sense of what 'small' means that you can get from seeing it in a Gigapan.
I thought ZnO crystals were a well known demo specimen for SEM work. At least when I was at Cornell in 1975, they were a favorite item for demonstrating the power of a SEM. I remember going to the SEM lab on Olin Hall with a friend who had bought some cheap SEM time at 2:00 AM. The most memorable item we looked at was the ZnO smoke sample.
Zinc burning in air forms perfect tetrahedral pointy crystals in a broad range of sizes that resemble a caltrop from outer space. See:
http://embedded.eecs.berkeley.edu/caltrop/pic/caltrop.jpg
I thought I'd have no trouble finding an image of these crystals, but an extended Google search didn't bring up a single example. Perhaps they have been forgotten. It would be interesting to see them again.
You might want to try some zinc oxide crystals. They form amazing three dimensional tetrahedral structures. I saw them with a SEM a lifetime ago.Aside from the whole 'very toxic' thing this sounds fun.
You can make it by igniting a thin strip of zinc metal (rescued from the shell of a dead cheap carbon-zinc battery). It burns like magnesium, but with less enthusiasm.
The thick white smoke is very toxic to the lungs, so don't breathe it. It should stick to a glass microscope slide without much encouragement.