How did alchemy emerge as an almost full-blown alchemy?

The first writers of alchemy seems to have a full blown version of alchemy in mind. This was around 100 A.D. with the Stockholm Papyrus and the Leyden X papyrus. Both of these seem to be written by the same author, and are "recipes" of alchemical transformations. They even admit when the transformation isn't real, but in appearance only. They are clearly based on some early philosophical ideas of transformation form Plato and Aristotle where the transformational steps determine the resulting material, and the starting material is non-consequential.

These are advanced ideas of how matter behaves. So how is it the first authors are using these ideas? Are we simply missing an entire multi-hundred years writings on the topic? I doubt it. These ideas, had they existed, would have ended up in one or many of the Alexandrian libraries of Hellenized Egypt, and would have been dumped by the Islamists from libraries like Oxyrynchus. And there is nothing in those dumps we didn't already have. 

We do have references to earlier writings, particularly those of Maria the Jewess, but that's one author, which could be missed in history.

How alchemy comes about remains a mystery. To me anyway. This chapter is about the ideas on the origins of alchemy.