On Minerals

Now, however, we must speak of those properties which happen to stones of their own accord. The properties original: "accidentia," referring to non-essential characteristics like color or texture that primarily happen to stones in general are many; however, the first among them is the mixture of matter. Let us say that if the matter is excessively dry, then it will not be well-mixable; and then either the place will be more porous and not solid, The generation of a pebbly stone. or it will be solid. If it is not porous but solid, it generates a single pebbly stone; when it takes it up in this way, displaying small bean-like grains; which diversifies the form through the amount of dryness and the heat coagulating it: because sometimes it perhaps wears down into gravel when much heat has dried it out. And if the place is very porous, through which the cooking heat exits everywhere Generation of gravel. Generation of small stones. through the oily earth, then that heat divides that matter into small pieces and cooks it into minute gravel. And if the matter were very viscous, then once divided, it reduces into small pebbles of various sizes which are very hard and of diverse colors because of the diversity of the matter. However, stones which, when they are cut, are polished to an excellent flatness and the dust which is scraped off is very fine, are made from matter that is excellently mixed, in which the moisture first worked to make every part of the dry matter flow to every other part; and afterwards the trapped moisture was dried out; and therefore such a stone is well-mixed. For a subtle moisture is easily mixable since it is capable of penetrating parts and the parts of parts, as was said in the second book of On Generation original: "sc[un]do pigeneos," referring to Aristotle's Peri Geneseos Kai Phthoras (On Generation and Corruption).. Above all, however, those stones are well-mixed which are mingled by way of vapor; and those, above all others, polish well and are made splendid, because the substance of the vapor already verges toward the subtlety of air and moisture: and these two are more subtle and more mutually penetrating in the form of air than in the form of water and earth. From these same causes come good compaction and continuity, as well as their opposites. For whatever matters are excellently mixed—unless the boiling heat dries out the moisture—these have the best continuity and strong compaction. A sign of this is found in the works of art The author uses "art" to mean human technology or craft, which mimics nature. which change nature: for those who make bricks of clay first mix into the earth some things which make the parts cohere, such as horse dung and things of this sort; and once the matter is made glutinous, they strive to mix these excellently; and the better these are mixed, the smoother and more compact the stones become. Potters do the same, who do not take just any earth but a tenacious kind called glis A Latin term for a type of thick, sticky clay. in their matter when they wish to fashion things from clay; they mix it excellently before they mold it; and then they allow the moisture to reside in it for a time, and they draw out the superfluous moisture in the sun, and thereafter they coagulate the vessels in the fire by the "digestion" In alchemy and medieval science, "digestion" refers to a process of slow heating. which is called optesis original: "optesis," a Greek term for baking or roasting in a kiln.. It is necessary, therefore, for nature to have this same method in the mixing of stones. Therefore, the earth is first penetrated by moisture, either bodily or spiritual; and then the superfluous moisture is separated from it, and after a long time, the binding moisture becomes sticky within it, which cannot be extracted by the baking heat; this matter, through such digestion, is turned into stone. And if there is found earth that is sometimes not completely glued together next to those stones, we know that such matter has been sufficiently acted upon, and therefore remained undigested. However, the kinds of stones that are made from water—which has been acted upon by terrestrial dry cold—are excellently compacted and seem almost polished, because water is among those things that are polished, and any part of it flows into any other and is coagulated in such continuity and frozen into stone. Let this be said regarding the mixing of stones.

Chapter One: On those things which are well and poorly mixed.

The method by which the colors of stones are determined must be taken from the book On the Senses and the Sensible A reference to Aristotle’s De Sensu et Sensato.; the science of which we shall hand down below at the opportune time, and therefore the things we assume here will be made manifest there. It is assumed here, therefore, that everything which is transparent in any genus of bodies is caused by many parts of transparent bodies which come into the composition of the body that is transparent. Furthermore, whiteness is caused by many transparent parts determined in another thing. The cause of transparency in pebbles. Blackness, however, comes from opaque parts of the body suppressing the transparent parts which are in the same body. Intermediate colors, however, are caused by the composition of these in three ways, as will be handed down in the science of the generation of sensible things. Let us say, therefore, that all transparent stones are caused by much matter of air which has been frozen and aggregated by the terrestrial matter taking hold of it: and if that transparency is not of any color but remains the transparency of air or water, then it is a sign that only excellent coldness took hold of the matter; and this is like the transparency of crystal, and beryl, and adamant The "adamant" usually refers to the diamond, prized for its hardness and clarity., and the stone called the iris A type of stone, likely quartz, that produces a rainbow effect when held to light.; but they have a difference in transparency and watery nature, since crystal seems not only to have the matter of water, but a wateriness declining into sharpness, because of which it is extremely transparent and declining toward brightness. Beryl, however, declines more toward water, for where it is turned, great drops of water seem, as it were, to flow. Adamant, however, has a wateriness drawn more toward the terrestrial dry, because of which it is darker and very hard, so that it strikes other metals because of its steely hardness; for steel also consists of wateriness and a very dry terrestrial nature. And therefore it also happens that the adamant stone, when it has a sharp angle, cuts and conquers all iron and penetrates every metal in cutting. The iris stone, however, is made from water that is almost like dew, which is frozen partly from vapor and partly from resolved dew. And therefore, when placed in the sun, it depicts the colors of the rainbow original: "colores vridis," though referring to the iris/rainbow effect. on the opposite wall. Stones similar to these are made from similar materials. For next to the banks of rivers, stones are very frequently found...