The First Matter ... vast and difficult subject. One can actually perceive the extraordinary difficulty of this concept only, - paradoxically - after completing the 'whole thing'. Because, when you don't know what it is, it is simply this : ignorance. And being ignorant is a simple state.
We can find our mercury in minerals - but not as you think it could be found. We just have to know exactly how to trick the whole thing in order to art-ificially extract the Spiritus Mundi out of it. OR to be able to use them as "philosophical bridges" and "Philosophical keys".
But, minerals and all this stuff are not the First Matter. First mean, actually, "FIRST".
Of course, from another point of view, they are the First Matter, but under a *particular* form. So, we say it is not the First Matter, as Pure First Matter.
Yes it is cheap, yes it is everywhere. Cheap because it is everywhere, for everyone. Everyone, everything catch it unconsciously.
A lot of matters are involved under the term of First Matter. Sometime it is a First Matter to use in the process. But, only in order to have the True, Pure, First Matter.
Do not misunderstand the terminology, it is not a fix one, they had not the same codes for their pointers, it is the scientific mind of today that biased this. Authors, depending of their reliance to some schools of arcanas, or to some authors, etc, will use the terms differently, form is not important, the essence behind form is primordial. First Matter can be a lot of things. You can only have a good discrimination when, again, paradoxically, 'you get it'.
This 'vapour', is not exactly a vapour at first. It behaves like it, yes of course. It comes out of the gate of the Axis Mundi and the Perpetuum Mobile. With a system of flux, and cycles. We can see it in the Macrocosm, and recreate it in the Microcosm. Pure, simple imitation of Nature.
Imitate what you can see behind the curtain of Nature's Expressions.
Yes understanding the Book Of Nature's Expression (BONE), and the Principles Of Life's Expression (POLE), can be difficult but it is a necessary part to learn (and you'll have to unlearn so much, and stay with this capacity to unlearn, even when you think you get it, because nothing is more dangerous than certitude in alchemy, always embrace the paradox in your vision, because sometime you'll need to embrace both possibilities, and both are right) - I was saying, a part to learn before having a serious work in the lab. Nothing actually mature can come out of the Lab without a strong, firm, mature, vision of the Nature's Laws/Expressions/Principles/ etc ... You can cross the right path without seeing it, because you're blind ! Rearrange inside, and everything rearrange outside. And you can see it. You need a P.H.D in Hermetical Vision okay ? Or, you need a good friend. Or you need a direct Wifi Link with Nature Spirit. Or you can be a reincarnation of Paracelsus or of Hermes Trismegist (this one is ... less possible). Anyway, the Wifi Link must be sustained. Cultivated. And you can only have it if you have a strong need to know. Hermetical Vision, this capacity to reach this place behind the curtain, is a marvellous capacity to unfold the mysteries of the Universe. The goal is NOT the Stone. The goal is Fusion with everything. The Stone is just a mean to an end. Nothing else. Just a piece of matter, chewed by "Spititus Mundi".
We have to know that a specified matter will never give more than what it can give in essence, because a specification will only lead to a higher specified matter. If you have gold, then you'll have exalted gold. If you have silver, then you'll have exalted silver. Gold will act in you as gold can, in the gold's realms. Silver will act in you as a lunar force, and will not touch anything else, because it is beyond its scope of action. And so on. Ask gold if it can act upon the lunar side in you, and it will answer you 'ask Luna ! This is not my job !'. Everything will depend on the Source of the Matter you'll use. Generally of course, Gold or a seed of Gold is used - it is present in ALL kingdoms. Depending how one will work. But the best thing is to have the First Matter's Gold Seed. Because it comes from the Central Fire/Sun, it is Universal, and can lead you to the Universal realm, and Universal means that it can have an effect upon all the sides of creation, because it is actually the source of all "metals" or "planets".
And here is the trick : a specified macro or microcosm can give you a universal agent. Depending how you'll treat it. And some are easier to work with.