Et:

Later today I'll go upstairs and get the book I read so I can summarize the oxygen information. I'd never realized that oxygen is a varied thing.

Here's a bit from the Britannica on frost:

"True crystalline hoarfrost is of two classes, one of which assumes columnar forms and the other of which assumes tabular, or platelike, forms. Generally the crystals of these two classes do not occur together on a single night; rather, one or the other will greatly predominate. Columnar or needlelike forms are found at the higher subfreezing temperatures, whereas plate crystals predominate under colder conditions. In their pristine state both forms are hexagonal crystals, the columns having a hexagonal cross section and the plates appearing as flat hexagons. Because they must grow outward from some supporting object, they rarely assume the perfect symmetry found in many snow crystals.... At very low temperatures, cubical crystals are sometimes found. "