A mold, almost ;)

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Sodium benzoate (a widely used food preservative, E211) was dissolved in water/DMSO mixture, and single droplets of the solution were evaporated on a glass slide. Field of view 2-4 mm

Glycine

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One of the stranger microcrystal forms I’ve ever seen. I have no idea what causes those curved shapes, no constraints seem to be present. They were obtained from saturated water solution of glycine in very thin layer.

Tartaric acid

Of the many organic compounds that can look good after crystallization from a melt, tartaric acid is unique. It melts at 172 deg Centigrade, low enough to be attained at glass slide heated by small flame, like a lighter. After cooling down it takes a couple of hours to crystallize. Here shown during the process. The grey area is still a glass phase. Note the fractal-like structure formed in a gas bubble.