6dc5455c____The_Coppermind___17th_Shard__Entry
[Chapter] 78 [Entry] 
It may seem odd to those reading this that atium was part of the body of a god. However, it is necessary to understand that when we said "body" we generally meant "power." As my mind has expanded, I've come to realize that objects and energy are actually composed of the very same things, and can change state from one to another. It makes perfect sense to me that the power of godhood would be manifest within the world in physical form. Ruin and Preservation were not nebulous abstractions. They were integral parts of existence. In a way, every object that existed in the world was composed of their power. Atium, then, was an object that was one-sided. Instead of being composed of half Ruin and half Preservation—as, say, a rock would be—atium was completely of Ruin. The Pits of Hathsin were crafted by Preservation as a place to hide the chunk of Ruin's body that he had stolen away during the betrayal and imprisonment. Kelsier didn't truly destroy this place by shattering those crystals, for they would have regrown eventually—in a few hundred years—and continued to deposit atium, as the place was a natural outlet for Ruin's trapped power. When people burned atium, then, they were drawing upon the power of Ruin—which is, perhaps, why atium turned people into such efficient killing machines. They didn't use up this power, however, but simply made use of it. Once a nugget of atium was expended, the power would return to the Pits and begin to coalesce again—just as the power at the Well of Ascension would return there again after it had been used.
The Hero of Ages/Epigraphs - The Coppermind - 17th Shard
Entry