Complete Works, Vol. V

however, has more wateriness drawn toward the dry terrestrial; because of this, it is darker and very hard, such that it collides with other metals except for the hardest steel, for steel itself is also of wateriness and very dry earthiness. And therefore it happens that when the diamond stone has a sharp angle, it cuts and slices all iron, and penetrates every metal in cutting. The iris [rock crystal/prism], however, is made from water as if it were already dewing, which is coagulated partly from vapor and partly from resolved dew. And therefore, when placed in the sun, it paints the colors of the rainbow on the opposite wall. These stones are made from similar materials. Indeed, near riverbanks, one very frequently finds stones of obscure transparency, according to the greater and lesser degree, whose color is caused by nothing other than the transparent, or that which is composed with it, or mixed with dark earth in part or in whole. Because it is easy to know the cause of these colors from what has been said, I pass over them. Black color in stones is very frequently caused by burnt earth; for this reason, black stones are also frequently very hard, and they are more polishable than they are cuttable. For this color is not caused by anything other than the privation of the transparent in the mixture, as will be evident when the science of colors is treated. Intermediate colors are red in kind, green, and yellow, and their differences. And as will be said in the book On Sensibles, red will be when a thin, ignited smoke is infused over the luminous transparent. This is found in certain stones which are called aquatic hyacinths, and in three kinds of carbuncles; for this reason, they are all said by Aristotle to be hot according to their nature. They differ, however, in redness; for if there is much transparency and the superimposed smoke is very thin and lucid, it is the color of that which is called palatius palatine/pale red. But if there is much transparency and the smoke is like an ignited, thick fire, then it is the color of that which is truly called a carbuncle;

and therefore, the one that truly reaches its species shines in darkness like a glow-worm original: "noctiluca", especially when clear and limpid water is poured over it. If, however, the transparency is somewhat thick, and the supernatant smoke is somewhat darker, it will be the color of that which they call garnet, because it is colored in the manner of a pomegranate grain. Aristotle calls all three of these carbuncles, and he says the garnet is the nobler and drier among them, even though it is of less value among gem-cutters and artisans. The one that is called by some an aquatic hyacinth has a color that is composed of limpid aquatic transparent, and not airy; and it has a superimposed ignited aquatic smoke, such as exists in a cloud of the sky, and not in the dawn. In the same way, we shall find the colors of transparent stones that are of a yellow color. For if the stone is of a transparent substance, and very clear, and has mixed into it subtle, highly burnt earth, then it will be the color of the clearest sapphire, and it will have differences of colors according to whether that transparent substance with that subtle burnt earth is clearer or darker. For a clear and pure yellow color is undoubtedly caused by much transparent material, since the vision penetrates into it, such that the light does not obstruct the vision, nor does anything luminous. If, however, with such burnt, vaporous earth there is somewhat thick watery transparent material, then the color of the hyacinth results, which is sufficiently less clear than the color of the noble sapphire. A sparkling and azure color is caused by a lucid transparent that is overlaid with thin and moderate, ignited watery vapor, and this is the green color which is called topaz; and in any stone where veins of golden splendor are found, such as in chrysoprase and chrysolite, the color of those veins is generated from the same cause. There are many transparent stones that are green, such as emerald, chrysolite, and the stone called prama, although there is a diverse greenness in them. The colors of all these