Book I Minerals color, taste, odor , physical properties of gemstones and minerals such as emeralds, diamonds, rubies, sapphires Page 31



	BOOK I	19

	melt in a fire. The molten metal, on cooling, again becomes hard and returns to its original form. In this way it differs from a stone that melts in a fire. The molten stone becomes hard when cool but does not return to its original form and appearance. There are reported to be six species of metals, namely, gold, silver, iron, copper, tin, and lead. Actually there are more. Mercury is a metal although we differ on this point with the chemists. Plumbum cinereum (gray lead) which we call bisemutum was unknown to the older Greek writers. On the other hand Ammonius writes correctly many metals are unknown to us, as well as many plants and animals. Stibnite, having been smelted and refined in a crucible is seen to belong more properly to the genus of lead minerals, tin, lead, and bismuth, than writers think. Moreover, having been refined in this manner and added to tin in the proper proportions, it produces the alloy libraria. Libraria is used by printers to make type.⁵ Actually each metal has its own characteristic nature which it retains when parted and separated from those metals with which it may have been mixed. Thus, neither electrum nor stannum is in itself a metal but a mixture of two metals. Electrum is a mixture of gold and silver; stannum, lead and silver. If the silver is parted from the gold, gold remains, not electrum, if parted from the lead, lead remains, not stannum. We cannot say whether brass occurs as a native mineral or not. The only brass known to us is the artificial product made from copper having been dyed with the color of cadmia fossilis. If any has been mined it has had the characteristic appearances of a metal. Aes nigrum and candidum are seen to differ from the rubrum species. Thus a metal is either solid or liquid. Mercury is the only liquid metal. Leaving the genera of simple minerals I shall now take up the mixed minerals. I shall not discuss all genera but only those that Nature has created from inanimate substances. In the class of mixed minerals I have placed those which have formed from two or three simple substances which are themselves mineral bodies. These are true minerals but with their constituents so mixed and combined in proper proportions that the smallest particle of the mixed body contains everything found in the body as a whole. They are so combined that if the mixed mineral contains three simple constituents or bodies, one can be separated from another by the force of fire, or a third from the other two, or two from the third. The two or three constituents are commonly combined in the new mineral in such a manner that the original character of none is evident. A composite mineral, even though it contains these same simple constituents, differs from a mixed mineral. The simple constituents almost always retain their form and one can be separated from another, not only by fire but also by water and sometimes even by the hand of man. Since these two things differ so greatly that one may be distinguished from the other I wish to distinguish them by those two names. I realize that Galen called an earth which con- ' Type metal is usually an alloy of antimony and lead rather than tin.