On Minerals

...they do not receive [mortar] well because their narrow pores do not absorb it; for this reason, stonecutters original: "lathomi," from the Greek for "stone-cutters" rarely use them in masterworks, and they say that these stones merely "praise" original: "laudant"; in this context, it implies the stones look good on the surface but do not bind structurally the walls. Other kinds of marble, however, are excellently mixed and vehemently "cooked" The author uses "cooked" or "decocted" to describe the geological process of stones hardening under Earth's internal heat; therefore they are hard and suitable for walls. But certain stones are more suited to buildings than others; when they are vehemently hard, their dryness is great and there is little moisture holding the parts together. When this moisture is congealed by cold, it leaves the exterior parts and flees to the interior. Such moisture is not well incorporated into the parts, and thus it moves easily to the interior and exterior. Because of this, after the compressing cold has made the moisture mobile, it is "drunk up" by the nearby heat of the sun, and then the stone splits apart. On the contrary, stones that are somewhat moist, with the moisture well-entangled in the members of the stone, dry out strongly in the air; therefore, they become harder and better for buildings over a long
Cause of the softness of tufa

duration of time. In tufa original: "thophis," a porous rock formed from volcanic ash or calcium carbonate, the cause of softness is moisture that has not been strongly extracted nor excellently mixed with earthy matter; therefore tufa is soft, and when placed in a fire it is not baked like a brick, but is turned into earthy ash. These things, then, are said concerning the hardness of stones; from these principles, other differences can easily be understood.

¶ Chapter five: On the workability and unworkability of stones.

From these points, the cause of workability original: "volabilitatis," referring to how easily a stone can be hewn or split along a plane and unworkability can now be made clear. For stones that are exceedingly hard are not easily worked, but rather crumble into small pieces; and when they do not have ordered pores, they do not split according to a "rule" A straight line or architectural guide. Just as knottiness occurs in wood from the diverse flow of the dry matter from which the body of the wood is generated, so it happens in stones from diverse mixing and the pouring-in of matter. This "knottiness" causes the stone to break inordinately and not according to a rule. Yet the hardest and driest stones, whether they are knotty or not, are more prone to crumbling than to being worked, because their pores are so tightened and constricted by dry-heat original: "optesi," a term derived from Aristotle referring to the process of baking or roasting by dry heat that their cleavage and division is taken away in different directions. However, those stones that are not constricted or hardened beyond a balanced state are easily worked and can be cut according to a rule, although they cannot be cut exactly like wood, but rather by small parts being drawn out while the rest of the body of the stone remains together. This, then, is the manner of a stone’s workability and unworkability. The very instruments of the stonecutters’ art show this: for stonecutters hew workable stones to a rule so that they "fly" split or smooth out across the whole surface; but it is sufficient that several angles of a rough rather than smooth surface reach the line, as they say the Lesbian masons A reference to the "Lesbian Rule," a flexible leaden ruler used in ancient Greece to measure irregular stones do, because on the island of Lesbos they find only stones that crumble.

¶ Chapter six: On the cause of porosity and compaction in stones, and of their gravity and levity.

In this same manner, one determines the cause of the porosity of stones and the cause of their compaction. For certain stones are found to be of such great porosity that they float upon the water, such as the stones thrown out by a volcano and certain pumices. Others are found to be most compact, such as precious stones and types of marble; and some are found to be midway between these. And indeed, the cause of porosity is nothing
Cause of the porosity of stones

else than that the moisture was not entirely mixed with the earthy matter but remained in different parts of it. Just as in a vessel, when the moisture has been "drunk up" by dry-heat, holes remain and the stone is made porous; because of the air trapped
Cause of compaction

in those holes, it floats upon the water. The compaction of parts, however, is chiefly caused by moisture penetrating the matter of the stone from all sides, which makes every part of it "flow" toward every other part, and thus the stone is made compact. This moisture is either bodily and watery, or spiritual and airy. And because the airy is more subtle than the watery, the substances of stones mixed from vapors are of greater compaction than those from other watery or earthy substances. Concerning the cause of the heaviness gravity or lightness levity of stones, it is superfluous to labor here, since this was sufficiently treated in On the Heavens and the World Aristotle's "De Caelo et Mundo", where it was shown why lighter stones sink under water while heavier wood floats upon the waters. These things, then, are said in general concerning stones.

¶ Chapter seven: On the cause of the multitude of small stones near shores, and the arrangement of bricks which are sometimes found on shores as if placed there artificially.

Beyond all that has been said, it sometimes happens near the banks of rivers and seas that a great multitude of small stones are found bound together as if by the strongest cement, as if they were taken from some wall; because of this, some people think that these were the works of the ancients, destroyed by the water. And what is more wonderful, along the whole length of a shore there is sometimes found an orderly row of bricks original: "laterum", as if they were placed there by art, though this does not seem to be a work of art because it is very
A wonder

extensive and does not have the form of any wall, but is merely brick next to brick with nothing above or below them. I say that the cause of the first of these two—namely, that small stones are found glued together as if by cement—is that those various flints were first coagulated, and in that place there was matter like burnt lime original: "calcis adusta" due to dry-heat; afterward, the inflowing water mixed it, and the stones, being "cooked" again by that same heat, were glued together. This cement is extremely hard, because whenever the dry earthy matter is calcined by dry-heat and then subjected to that heat again, it is made exceedingly hard, almost indestructible by fire. This, however...