Questions about Crystal Alum?

I have two questions about Crystal Alum that I need some help with. For anyone who does'nt know, Alum is a non-toxic chemical used primarily in Pickling, and in canning things. When you add X amount of powder alum to X amount of hot water, as the water cools/evaporates, the alum particles form together and create crystals. Now you all know what im talking about.

QUESTION ONE: Will crystal alum MELT in an OVEN? As in, If for whatever reason I please, I stick alum with something in an oven, will the crystals melt or deform in any way because they were made in an aqueous solution?

QUESTION TWO: As with any type of crystal, you can use a rock or similar substance to create a GEODE. Even an eggshell works for an Alum Geode. Would a clay-like substance work? For example. I use a clay type substance to mold something like the shape or a rock. Then I pour heated water/alum saturated solution into the "rock" mold. Then I seal the top, and poke a very tiny hole into the top, to allow the evaporating and escaping water release, and not BLOW UP instead. When the clay is hard and molded, and after a few days left alone, in theory the crystals form. Will they adhere to the clay and create a geode, or instead just make crystals that will slide around inside untill I crack it open and remove them?