On Minerals

...only insofar as they are in a state of transformation toward each other or toward other things—just as are clouds, rain, and snow—they would without a doubt not last long; instead, after a short time, they would resolve back into their elements. Yet we see the exact opposite happening in the natures of stones. Furthermore, we find virtues in stones that do not belong to any single element, such as the power to drive away poison, to expel carbuncles original: "antraces"; refers to inflammatory skin lesions or boils, or to attract and repel iron. Concerning these powers, as will be proven further on, it is the common opinion of all the wise that this virtue is a consequence of the species and form of this or that stone. It is certain, therefore, from these facts, that stones have forms and determined species.

These forms, however, are not "souls," as it seemed to some of the ancients. For, as we showed in the book On the Soul Aristotle’s De Anima and as was made clear at the beginning of the Physics, a soul does not perform only one single operation, but many, and it does so by its own nature rather than by accident. The nature of a stone, however, performs only one thing; and what it does, it does by necessity—which a soul does not do. Furthermore, the primary work of a soul is life, yet life is found in a stone according to none of its distinctions. For if a stone used food medieval science often compared mineral growth to biological "feeding", it would need to have pores and paths through which the nourishment could be absorbed into it. The very hardness and compaction of many stones shows this to be false, for they do not allow themselves to be divided or opened for the reception of food.

Moreover, if it used food, it would need to have some part that first draws in the nourishment, such as roots in plants or a mouth in sentient beings; we see nothing of these in stones. Nor is it correctly said that the soul of a stone is "oppressed by earthiness" and therefore unable to exercise life and sensation—as many physiologists have said—because according to this, nature would fail in necessary things by not giving stones the organs with which to carry out their necessary operations. Therefore, stones do not have souls, but rather other substantial forms granted by celestial virtues and the specific mixing of the elements.

The differences of stones

For the most part, these forms are unnamed, yet their differences depend on the various names of stones, such as when they are called tufa original: "thofus"; a porous rock formed from volcanic ash or calcium carbonate, pumice, flint, marble, sapphire, emerald, and the like. Since these are hidden from us, we do not have the proper definitions of stones except through roundabout descriptions, using their accidents accidents: non-essential qualities like color or hardness and signs in place of definitions.

A stone is of the genus of mixtures, but not "complexioned"

But we know this: since there are diversities in bodies that are simply movable and changeable and mixed, a stone is of the genus of "mixtures." Since, however, the genus of mixtures is divided into the "complexioned" biological mixtures with a specific balance of humors and the "uncomplexioned," we know that the stone belongs to the genus of uncomplexioned mixtures. Putting all these statements together, we say that a stone is a mixture, not complexioned, coagulated into a form by a mineral power. From this, it is further manifest that a stone is more of a "homogeneous" nature than something possessing life—even though different elemental natures exist essentially within it—which is why the science of stones precedes the science of complexioned things i.e., biology and medicine.

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There are many forms of stones, such as in the genus of porphyry marble, alabaster, and the like. It is similar in other kinds of stones which it is not useful to pursue here, because their forms will be made manifest below through the accidents of their body and hardness; for these accidents are proper to them, and once they are known, their nature is sufficiently manifest. One should not seek the "end" end: the final cause or purpose, because in physics, the form is the end. Therefore, since we consider ourselves to realize knowledge of a thing when we know its essential and proper causes, the nature of stones has now been known universally in a general sense. Nevertheless, since the place of generation is a principle (as was determined in previous sections), we must also know about the place of the generation of stones, because the place acts as a kind of efficient cause for the stone, or is where the formative power of the stone is first granted.

Chapter Seven: On the Recalling of Places in Which Stones are Generated.

Let us therefore make mention of the places in which stones are generated either always or frequently, and let us inquire into the power of those places and their differences. We see that many stones are found on the banks of perennial waters, and we know by this that the banks of certain waters are places that generate stones. Such banks differ, however, because some produce stones more quickly and some more slowly. For in certain places on the banks of the river called Gion The Gihon, one of the four rivers of Paradise, often associated by medieval scholars with the Nile or the Oxus, stones are generated in the space of thirty-three years, as Avicenna and certain other philosophers testify. Yet not all water is generative of stones on its banks, because the swampy water of corrupt earth corrupts stones rather than generating them. We see this in certain regions where, although they are watery places, they do not frequently generate stones.

Furthermore, we frequently find mountains to be stony, from which we know that in mountainous regions is a place for the generation of stones. However, we sometimes find mountains without stones, but those are generally neither large nor joined to other mountains, but are found solitary—so that perhaps there is only one, or at most two or three. Whenever many mountains are joined together, then stony mountains are found; and many stony mountains are also sometimes found on flat land with a solid surface. This cannot happen everywhere, and those specific places are generative of stones. Furthermore, stones are very frequently generated in waters, which can only be said because those waters are places for the generation of stones.

Rainwater is converted into stones.

A sign of this is that there are certain waters from which stones are generated when they are poured over the banks in which they flow; and if they are poured over another place, they do not generate stones from them. For it has been experienced in the Pyrenees that there are certain places in which rainwater is converted into stones; yet if it is poured elsewhere, it remains water and is not transformed...