Trioxane fuel tablet recrystalization I had a bunch of old military trioxane fuel tablets.  I decided to open all of the packets, maybe a dozen, and place the contents in an empty tin coffee can with a plastic lid.  I put the can in a dark closet.  I let it sit undisturbed for several months.  Upon opening the can, I saw crystal structures growing off of the sides of the tin can.  They appear to be of a lightweight somewhat flexible plastic composition and are flammable in the same way that the rest of the fuel is.  If I disturb them by damaging them or removing them, more will grow over time, if I let the container sit.  What is this reaction?  Has anyone witnessed this before?
It's subliming (aided in this case by decomposition) and re-depositing.

Substances that turn directly from solid to vapor (e.g. naphthalene, water ice) are said to sublime, rather than evaporate. The inverse, changing from vapor to solid, is termed deposition.

When water vapor deposits on very cold surfaces, such as "dry ice", it grows into amazing dendritic crystals: