Briefly speaking, the Philosopher's Stone is real, but it hasn't been accomplished as often in recent centuries as it once was. This is because the astrology is an integral part of it's creation, and the energy from the Stars hasn't been properly addressed. Another reason the creation of the Philosopher's Stone (a.k.a. The Sorcerer's Stone) isn't evident of late is that many alchemists tend to insist on comparing alchemy to chemistry, and thus think accordingly. Alchemy is more like micro-biology. Yeasts are microbes used in the vegetable work, and there are corresponding extremophile microbes in the mineral work.
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It is my opinion that the Philosopher's Stone is the product of extremophile activity. Microbes are sensitive to cosmic energies, like a magnetized needle floating on the surface tension of water. They are known to be able to transfer single electrons to create iron, and they are responsible for the majority of Earth's iron ore deposits. Mercury is one electron different than gold, they are next to each other in the Periodic Table of Elements. It's not difficult to surmise that there are microbes that can transmute mercury to gold.
Microbes also out number the cells in our bodies, and we are dependent on them for our health. Without microbes, there wouldn't be any higher life forms on our Planet. They are the first life, from and of, the first matter. In creation of the Philosopher's Stone the alchemist is not only purifying the parts, they are concentrating the microbes through propagation, and collecting the enzymes they create. It is the enzymes that affect the microbial mineral environment as a bi-product of their digestive process. The Philosopher's Stone is either a creation of the seed, enzymes, or the actual microbes themselves.
I explain this further in my handbook, and I list citations if you want to review my research.