Apparently there are fifty-seven "paragenetic modes," wherein a paragenetic mode is defined as a genesis for the creation of a mineral. One such mode would be

Apparently there are fifty-seven "paragenetic modes," wherein a paragenetic mode is defined as a genesis for the creation of a mineral. One such mode would be condensation directly to a solid from a gas in the context of "condensation at volcanic fumaroles." The bit about pyrites is that there are an astounding twenty-four ways you can make them. So, this looks like a new lens with which to examine and classify minerals, after going through a very large catalog of them tabulating each manner of formation allowed. Some of them are surface oxidation and weathering, some are stellar (!), and so on. Given that you can arrange at least some of these modes (why paragenetic?) in time order, you could look at what kinds of minerals, whole classes of them, could form and when, or as you put it, what era. I'm not sure of the utility of this, but then I'm not a geologist. Looks like a nifty classification method. Perhaps you could come up with "Incidence of mineral X ought to be correlated with incidence of mineral Y," although I thought that was already pretty exhaustive.