Breaking Bad New Season

I didn't see another thread for this, so I thought I'd see if there are any other fans out there in bt land.

It appears that they're not kidding with the tagline to the new season, "Walt used to be in danger. Now Walt IS the danger." (paraphrasing here)

Mostly I want to know, what the heck is up with Hank's mineral obsession? Did I miss something? Is it a healing thing or is it just the random thing he decided to cling to with nothing to do but surf ebay between therapy sessions?