TREATISE II

ON THE ACCIDENTS OF STONES.

CHAPTER I.

Now we must speak of those things which happen to stones by themselves. The accidents that primarily happen to stones in general are many. The first among them, however, is the mixture of matter. Let us say that if the matter is vehemently dry, then it will not be easily mixable; and then either the place will be porous, not solid, or it will be solid. If it is not porous, but solid, a very sandy stone is generated, which, when taken this way, produces sandy minutiae, which is diversified according to the quantity of dryness and the heat coagulating it.

Because sometimes it is perhaps rubbed into sand when great heat has dried it; and if the place is very porous, through which the heat cooking the unctuous earth exits everywhere, then that heat divides that matter into small parts and decocts it into fine sand.

And if the matter were very viscous, then being divided, it is reduced into small stones of diverse quantities, which are very hard and of diverse colors due to the diversity of the matter. Stones, however, when they are cut, are smoothed very well, and the dust that is abraded is very fine; they are from matter mixed very well, in which the moisture first operated, making every part of the dry flow to every other, and afterward, the apprehended moisture was dried; and therefore such a stone is well mixed. For the subtle and moist is well mixable, since it is penetrative of parts and parts of parts, as is said in the second Peri geneseos On Generation and Corruption.

Above all, however, those stones are well mixed which are mixed vaporously, and these are polished well and rendered splendid above all others; because the substance of the vapor already verges toward the subtlety of air and moisture; and these two are more subtle and penetrate each other more in the form of air than in the form of water and earth. From the same causes, there is good compaction and continuity, and their opposites. For the matter of those whose parts are mixed very well, unless the decocting heat dries the moisture, has the best continuity.