Complete Works, Vol. V

and strong compaction. A sign of this is found in the works of art that imitate nature. For those who make bricks first mix into the earth certain substances that make the parts cohere, such as horse dung and things of this sort; and once the material is made glutinous, they strive to mix these perfectly. The better these are mixed, the flatter and more compact the stones become. Potters do the same, for they do not use just any earth, but the tenacious kind called glis clay/loam, when they wish to mold something from mud. They mix it perfectly before they mold it, and then they allow the moisture to settle in it for a time, and they extract the superfluous moisture in the sun. Then, they coagulate the vessels in a fire by a process of digestion called optesis baking/roasting. Therefore, nature must also have this method in the mixing of stones. Earth is first penetrated by moisture, either corporal or spiritual, and then the superfluous moisture is separated from it. Afterward, for a long time, the moisture is thickened within it, and since it cannot be extracted by optetic baking heat, this material is turned into stone through such digestion. And if earth is sometimes found that is not completely glutinous next to those stones, we know that such material has suffered sufficiently, and therefore remained undigested. The kinds of stones that are made from water, which has been acted upon by dry, cold earth, are best compacted and appear as if polished, due to the fact that water is among the polished things, and any part of it flows into any other, and in such continuity, it coagulates and freezes into stone. Let this be said regarding the mixture of stones.

CHAPTER II.

The mode by which the colors of stones are determined must be taken from the book On Sense and the Sensible, the knowledge of which we shall deliver here in due time. Therefore, what we assume here will be manifest there. It is assumed here, therefore, that everything that is transparent in any kind of body is caused by many parts of transparent bodies that come into the composition of the body that is transparent. Furthermore, white is caused by many transparent things determined in another thing. Black is caused by parts of an opaque body oppressing the transparent parts that are in the same body. Intermediate colors are caused by the composition of these through three ways, as will be delivered in the science of the generation of sensibles. Let us say, therefore, that all transparent stones are caused by much matter of air and water, which, upon apprehending terrestrial matter, is frozen and gathered. And if that transparency is not of any color, but the transparency of air or water remains, then it is a sign that only excellent cold has apprehended the matter. This is like the transparency of crystal, beryl, diamond, and the stone called iris.

The difference between the matter of crystal and beryl.

But they have a difference in transparency and watery nature; for crystal seems to have not only the matter of water, but a wateriness declining into airiness, which is why it is highly transparent and declines toward clarity. Beryl, however, declines more toward water; hence, when it dissolves, it seems as if large drops of water are flowing. Adamant [diamond]