No, do not use a hyphen. 'Chemically' is an adverb that describes the manner in which tourmaline is deposited. It modifies 'deposited', which in turn, modifies tourmaline. Typically, we use a hyphen after the adverb 'well' when the next word is a participle acting as an adjective. For example:
a well-written book, a well-versed scholar
If the sentence is working fine on its own, don't congest it with unnecessary punctuation as hypens, semi-colons, or commas.
As far as helping the reader, grammar rules exist to do just that. They keep sentences from running on endlessly, give readers a chance to breath between clauses and lists of nouns with a well-placed comma, and keep readers from confusing subjects in a sentence. We should know the grammar rules well and not violate them on a presumption of what our readers will like. Being too liberal in one's style can give some readers the impression that the writer is uneducated. So, try to avoid making decisions about punctuation on a whim. It is important to keep a standard of writing.
Aesthetically, I would argue that hyphens make writing less pleasing to the eye.
Also, hyphens can be used to interject an entire sentence into another when there is some background information that the reader needs to know.
'Last summer this girl, Janie, and I-she was one of those tomboyish types who would sock you in the face if you gave her any lip-decided to go hang out with this other buddy of mine down by the lake.'