Gold During the Middle Ages
Geber's idea of the formation of gold scales and nuggets in situ in alluvial sands seems to follow from the Greek (Thales, Theophrastus) postulate that gold originated from water (in Geber's case from cupriferous waters). Onto that postulate has been grafted the alchemical idea (also borrowed from the transmutation concepts of the Greeks) that the sun was capable of transmuting the base metals (e.g., copper) into gold, as will be discussed in this text. Geber's theory that gold nuggets are formed in situ in eluvial and alluvial sands, when shorn of its alchemical fantasies, is not unlike present-day in situ accretion theories of the origin of gold dust and nuggets in placers.
Avicenna, the great Persian physician and translator of Aristotle, in his treatise De congelatione et conglutatione lapidum (de mineralibus) grouped minerals in a relatively modern way as stones (rocks), sulphur minerals, metals, and salts. About veins, he had little to say in detail, but he disagreed with Aristotle and the alchemists of his time about the role of transmutation of metals in the earth, holding to the idea that each metal was a specific type of earth (element).
It is interesting at this point to digress briefly and consider the various alchemical theories on the origin of mineral (gold) deposits. Alchemy is thought by some historians of science to have developed in China in the early centuries of our era and to have diff used through India to the Middle East and Alexandria; others consider a contemporaneous development in China and Alexandria more probable. The word al-chemi is evidently of Arabic origin and is said by some to mean black land (Egypt) in reference to the dark silty soil of the Nile delta. Another version contends that al-chemi is derived from the Coptic and means black art, as practised by the early chemists, who dealt essentially with the reduction of ores, the making of glazes and glasses, and the concoction of medicinal potions, all mysterious operations quite beyond the ken of most people of the time. The early Western alchemists were strongly influenced by Aristotelian views as well as by those of the astrologers, believing that the centre of the earth was a holocaust of fire produced by the focus of the rays of all the seven known planets upon the earth, which was considered at the time to lie at the centre of the universe. Thus, Apollo or Sol (the sun) gave rise to gold, Diana or Luna (the moon) to silver, Mercury to quicksilver, Venus the metal copper, Jupiter, tin, Saturn, lead, and Mars, iron. These views were held by many of the great alchemists of the time, Geber, Rhazes, Paracelsus, and Norton, and by many of the great scholastic philosophers of the period among whom may be mentioned Roger Bacon (1214-1292), Vincentius Bellovacensis (I 190-1264), Albertus Magnus (1200-1280), and his illustrious pupil, Thomas Aquinas (1225-1274).
Albertus Magnus (Albert of Cologne), Dominican, saint, and patron of the natural sciences, was one of the foremost philosophers of the middle Ages and wrote extensively on most aspects of philosophy and on a great variety of scientific subjects. During his long life Albert traveled widely, visiting many of the gold placers and mines in central Europe, as is readily apparent from his many writings. His knowledge of alchemy (chemistry) was, however, limited. One of Albert's works, De mineralibus (On minerals), written about 1260, is of particular interest in the present context. In this work, Albert embraced the Aristotelian view of nature, basing his science of mineralogy on the "four eternal cause§": material, efficient, formal, and final. As regards the material cause, the matter of which the minerals are made, his basis is the four elements (earth, air, water, and fire). After ranging over the field of rocks, he turns to the metals such as copper, lead, silver, and gold and discusses the places where these metals are produced and how they originated in deposits. His theory is essentially Aristotelian, onto which have been grafted many of the ideas of the medieval alchemists, as can be seen from the following passage taken from Wyckoff's (1967, pp. 182-183) translation.
The natural scientist seeks to understand the cause of all these things; and, as we have said in the science of stones, the place produces things located in that place because of the properties of heaven poured into them by the rays of the stars. For as Ptolemy says, in no place does any of the elements receive so much of the rays of all the stars as in Earth, because I Earth] is the invisible centre of the whole heavenly sphere; and the power of the rays is strongest where they all converge; and therefore Earth is productive of many wonderful things.
In order to know the cause of all the things that are produced, we must understand that real metal is not formed except by the natural sublimation of moisture and Earth, such as has been described above. For in such a place, where earthy and watery materials are first mixed together, much that is impure is mixed with the pure, but the impure is of no use in the formation of metal. And from the hollow places containing such a mixture the force of the rising fume opens out pores, large or small, many or few, according to the nature of the [surrounding] stone or earth; and in these [pores] the rising fume or vapour spreads out for a long time and is concentrated and reflected; and since it contains the more subtle part of the mixed material it hardens in those channels, and is mixed together as vapour in the pores, and is converted into metal of the same kind as a vapour.
In a later passage, Albert discussed his ideas on the precipitation of gold. Further, in Wyckoffs translation (P. 233) we read:
Albert's concept of the origin of placer gold is of considerable interest because he was evidently the first to clearly outline an in situ chemical accretion for gold dust and nuggets in alluvial deposits. Again from Wyckoff's translation p. 184 we read:
"But gold which is formed in sands, as a kind of grains, larger or smaller, is formed from a hot and very subtle vapour, concentrated and digested in the midst of the sandy material, and afterwards hardened into gold. For a sandy place is very hot and dry; but water getting in closes the pores so that the vapour can not escape; and thus it is concentrated upon itself and converted into gold. Therefore, this kind of gold is better. And there are two reasons for this: one is that the best way of purifying Sulphur is by repeated washing, and the Sulphur in watery places is repeatedly washed and purified; and for the same reason the earthy Quicksilver is often washed and purified and rendered more subtle. Another reason is the closing of the pores underneath the water along the banks; and thus the dispersed vapour is well-compressed and condensed, and is digested nobly into the substance of gold, and hardens into gold."
Rafal Swiecki, geological engineer email contact
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