Microscopy plays a big part in geology, whether it's picking out forams for biostrat, describing microfacies in carbonates, point-counting grains in a sandstone, or identifying metamorphic mineral assemblages. But along with the academic value of microscope work, I think we can all appreciate the aesthetic beauty of these micro-worlds.
I recently ran across the Nikon Small World contest, which allows people to submit photomicrographs of really small stuff, which are then judged on their beauty and composition. There 2008 winners (and honorable mentions) are up, and show lots of really cool images of a variety of subjects. Unfortunately, I didn't see any strictly geological examples out there, which is a shame; you'd think someone would have a picture of a schist with crossed polars out there! I think the 2009 competition needs some geo-representation.
Anyway, I nabbed a few of the really slick ones from this year for your viewing enjoyment.
This is a cute little diatom, just kicking back and relaxing on a branch of red algae (100x):
I think diatoms must be a favorite, since there are several of them; here are some, along side some Closterium and Spirogyra (40x):
Showing some silacecous love, here are some radiolarians (160x):
More diatoms (100x):
And, finally, something near and dear to grad students everywhere, caffeine crystals (400x):