On Minerals

9 On Minerals

T stones (Colgrave and Mynors, 1992). Rabbi Chisdai Abu-Yusuf made much

he mineral and metal resources of Europe were known and celebrated from an early date. Bede’s description of Britain lists copper, iron, lead and silver among its metals and amber and jet among its semi-precious

of the silver, gold, copper, iron, tin, sulphur, porphyry, marbles and crystal of Al-Andalus (Adler, 1987: 26). Arab geographers also reported on the resources in other parts of the Islamic world too. Al-Muqaddasc’s description of Syria noted iron mines around Beirut and red sandstones near Aleppo; in Palestine quarries of white stone and marble; in the region of Ghawr sulphur mines; and the recovery of salt from the Dead Sea (Collins, 2001: 154). Such accounts appear to imply relatively large-scale exploitation by the late tenth century. Exploitation of mineral and metal resources in Europe at this period tended to be more local in extent and restricted to the working of shallow or exposed deposits. The discovery of rich silver-bearing ores, first at Goslar in the Harz mountains of Lower Saxony in the mid-tenth century, and more importantly those at Frieberg in the eastern Erzgebirge during the twelfth century, however, prompted a boom in mining and prospection. By the end of the medieval period, mineral and metal extraction was being undertaken on an industrial scale often from deep mines. Gold was found and extracted from veins in the Alps and the Balkans. Further discoveries of silver were made in the Carpathian mountains, in Alsace, the Spanish Meseta, and south-west England. Important deposits of lead and zinc were found in the Ardennes, and iron in the Low Countries and northern Italy, and the long tradition of

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tin production in England was revitalised (Riddle and Mulholland, 1980; Long, 1999; Radkau, 2002).

Explanations for the physical formation of stones, minerals and metals are almost entirely absent among European writings before the thirteenth century. One slightly tangential exception was salt. Why sea water should be salty intrigued those interested in natural phenomena. Both Isidore and Bede posited, following Pliny the Elder, that under the evaporating action of the

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sun, water became denser and more bitter (Fontaine, 1960: 308; Kendall and Wallis, 2010: 96). Adelard of Bath extended this idea. Using the analogy of extracting salt from a pan of brine over a fire, he explained that it was during the passage of the oceans through the torrid equatorial zone that most of this evaporation occurred, whilst seasonal differences in the salinity of seawaters resulted from the subsequent localised effects of the sun in different parts of the world (Burnett, 1998: 185–7). Rarely was the origin of this salt sought, but this critical issue was dealt with by William of Conches who stated that as water penetrated through soils and rocks it picked up certain of their qualities. Thus water passing through sandy and stony ground would become sweet, water passing through sulphurous, chalky or metallic soils would become bitter, and that which percolated through salty ground, saline (Ronca and Curr, 1997: 113–14).

When it came to metals, one of the very few to offer a theoretical explana- tion was Hildegard of Bingen. Writing in Germany only a generation after the discoveries at Frieberg, it is difficult to ignore the probability that it was the mining activities themselves which had rekindled interest in formation pro- cesses. A product of its time, Hildegard’s explanation found in Physica drew heavily on the workings of the elements:

. . . where the fiery power that flows in water penetrated the earth, the fire of the water transformed the earth into gold. Where the purity of the flooding water penetrated the earth, that purity transformed itself and the earth which it suffused into silver. Where the fluctuation of the water penetrated the earth, moved by the wind, it and the earth it transfused were changed into steel and iron . . .

(Throop, 1998: 237)

Hildegard’s account of the creation of precious stones, however, appears to have more in common with fable than natural philosophy [Doc. 19]. These, she stated, all originated in the east. Here mountain streams were boiled by the heat of the sun. When these occasionally burst their banks the waters were turned to sticky froth on contact with the surrounding rocks. Over the course of a few days this foam would harden and eventually dry. Variations in the length of daylight and temperature during this process gave each stone

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its particular colour and properties. Eventually these gems would fall from these rocks and embed themselves in the surrounding sands. When the rivers next flooded, these precious stones were washed out and carried around the world to the various locations where people were known to find them (Throop, 1998, 137–8).

The space left by the absence of empirical evidence, particularly with reference to gemstones, was more than filled by the medieval creative imagination.

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These were variously said to originate in the four rivers emanating from Paradise so often shown on mappae mundi, in the streams of the mythical land of Cockaigne or in the gravelly sea of the land of Prester John (Lee, 1952). One of the more enduring stories concerned the challenges facing those looking to recover diamonds. In a tradition stretching back to the Arabian Nights, the sailors’ tales compiled by Captain Buzurg spoke of a burning and inaccessible valley protected by snakes in Kashmir where they could be found. Unable to descend because of its many imminent dangers, men of low caste instead elicited the aid of vultures to retrieve the precious stones by throwing the butchered parts of lean sheep into this chasm. Occasionally diamonds would adhere to these joints. Carried off by the vul- tures, these men would follow the bird in the hope that diamonds would fall out during its flight (Freeman-Grenville, 1981: 75). The essential elements of this story would be repeated by Marco Polo nearly three centuries later although here it was said that the men would chase the birds away from their prize to recover the diamonds, or, if the meat had been consumed, they would follow the birds to their nests and recover the stones from their excreta (Komroff, 1982: 297–8). An alternative was provided by Sir John Mandeville, who claimed that diamonds grew in what appears to be an organic way on outcrops of crystal: ‘They grow together, male and female, and feed on the dew of heaven and continue and breed, and they make children beneath them, which multiply and grow each year’ (Tzanaki, 2003: 105).

Such stories entertained their medieval audience but for some at least they stretched credulity. Al-Birunc was one such doubter. In discussing rain stones in his major work on minerals he brought into question not just earlier authorities such as al-Razi and Ibn Zakariyya but also highlighted the gullibility as well as ingenuity of ordinary people. He described the powers of this stone to cause rain as ‘imaginary’; he admonished other scholars for not checking their facts; he embarrassed individuals who had tried but failed to use the stone in his presence; and even suggested that one community had exaggerated the stone’s properties in order to encourage others to remove them from their fields in order to improve their agricultural potential (Said, 1989: 188–90). What is certain is that the scholarly texts emanating from northern Europe during the first half of the middle ages, whilst easily dif- ferentiated from the literary tradition, nevertheless contained much that

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was exotic and magical too.

Most early medieval mineral and metal lore in the west derived from a narrow but eclectic set of Classical sources. One such was a first-century Greek text on the magical qualities of stones by an otherwise unknown, Damigero, adapted into Latin by the fifth century. But the most important was undoubtedly Pliny the Elder’s treatment of the subject in books 33 to 37 of his Naturalis historia transmitted either directly or through either Solinus

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or book 16 of Isidore of Seville’s Etymologiae (Barney et al., 2006: 317–36). Typically each individual entry provided details of shape, colour, geographic occurrence, indications of their physical properties (hardness, flammability, etc.) and potential uses for apotropaic and medical purposes. The latter were dealt with in more depth in the last section of Dioscorides’ De materia medica. Here brief descriptions were provided of colour variations, brittleness and malleability, and again where they could be found. But Dioscorides’ main concern remained how earths, minerals and other chemical compounds should

be prepared and against what ailments they proved most efficacious (Osbaldeston, 2000: 781–830). In combination these works spawned one branch of one of the most popular literary genres of the middle ages – the lapidary.

The most influential of lapidaries that drew upon these authorities was that compiled by Marbode, bishop of Rennes in the early twelfth century. Written in metrical form it was immediately popular and would become the basis for an enduring lapidary tradition in France and elsewhere down to the end of the medieval period. Entries for jasper and beryl are typical of the content and scope of the Liber lapidum seu de gemmis – what mattered was the stone’s virtues and powers:

[ Jasper] There are, they say, seventeen types of jasper. They say that there are many colours and they confirm that it is made in many places in the world. The best is that which is green and translucent: everyone agrees that this is the one which possesses the greatest virtues. Piously worn, it drives away fevers and water retention; placed next to a sleeping woman it protects her and helps during pregnancy. If blessed, it gives grace and power and it is believed chases away dangerous spirits. Its force is greater than that of silver.

. . . [Beryl] What gives beryl its sparkle is its hexagonal shape: were it not for this its shine would be dulled. Some maintain that the most eye- catching of these resemble oil that floats on water. This stone comes to us from the Indies. It is said that it promotes conjugal love and that it strengthens those who wear it. It burns, they say, the hand of those who hide it in the palm. Put in water this helps to cure eye disease and if one drinks it, it prevents burping and hiccups. It also soothes all ailments of the liver. Experts are of the opinion that there are nine types of this stone.

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(Translated from Monat, 1996: 23, 31)

Other lapidarists took their cue not from Classical sources but from two lists of precious stones found in the Bible. Both were a regular subject for early biblical exegeses such as Augustine and Jerome. The first related to the description of Aaron’s breastplate, the so-called 12 stones of the pectoral, found in Exodus 28:17–20:

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And you shall set in it four rows of stone. In the first row will be a sardius stone, and a topaz and an emerald; in the second a carbuncle, a sapphire and a jasper; in the third a ligurius, an agate and an amethyst; in the fourth a chrysolite, an onyx and a beryl.

It was more common, however, for lapidaries to use as their basis the 12 stones of the apocalypse or heavenly Jerusalem found in Revelation 21: 19–21:

And the building of the wall thereof was of jasper stone: but the city itself pure gold like to clear glass. And the foundations of the wall were adorned with all manner of precious stones. The first foundation was of jasper; the second, sapphire; the third, a chalcedony; the fourth an emerald; the fifth, sardonyx; the sixth, sard; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprase; the eleventh, a hyacinth; the twelfth, an amethyst.

Their allegorical meaning was treated in works such as Bede’s Explanatio apocalypsis (Explanation of the Apocalypse). The green of jasper stood for the ‘unfading verdure of faith’ and was capable of putting ‘to flight vain fears’, the pale light of chalcedony was symbolic of those who practised their faith modestly, and sard’s ruddiness was emblematic of the glory of the martyrs (Marshall, 1878; Kitson, 1983). Using such images in this way, the Apocalyptic Lapidaries complemented the treatment of animals to be found in Physiologus. Indeed this work too had included certain stones among its beasts – the agate stone, pearl, adamant, Indian stone and magnet (Curley, 1979).

Just as bestiaries expanded upon Physiologus, so lapidaries quickly became enlarged. Marbode’s work contained descriptions of 60 precious stones, and the earliest surviving Old English lapidary written around the same time appended brief entries for 10 stones to those of the Apocryphal dozen (Evans and Serjeantson, 1933: 13–15). In the hands of later encyclopaedists these numbers grew ever greater as they combined the two parallel traditions. Bartholomew the Englishman included descriptions of 103 stones and metals arranged alphabetically in the tenth book of his magnum opus (Seymour et al., 1975: 825–81). The wealth of sources that mid-thirteenth-century compilers could draw upon is graphically illustrated in book eight of Vincent

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of Beauvais’ Speculum naturale. Here the three great Roman works – Pliny’s natural history, Solinus’ wonders and Dioscorides’ medical manual – shared space with Arnold of Saxony’s De finibus rerum (The Purposes of Things), Bartholomew the Englishman’s De proprietatibus rerum, Thomas of Cantimpré’s De natura rerum and an unspecified lapidary. Tellingly, Vincent also included references to the works of Aristotle and Avicenna (Vincent of Beauvais, 1494: 82–91). It was through these two authorities, and a third work by Theophrastus

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entitled De lapidibus (On Stones; Eichholz, 1965), that crucial advances came to be made by European scholars regarding the origins of stones and metals.

Aristotle, of course, had long been available in the Arabic world and his influence can be detected in almost everything that was written on stones and metals in this cultural and religious milieu. Aristotle’s theory on the formation of stones and metals was laid out in books three and four of his Meteorologia (Meteorology; Lee, 1952: 287–9; 318–25). Two principles applied. The first was the action of two ‘exhalations’ or vapours, one wet and one dry, generated by the energy of the sun. Underground and through interaction with the earth these became compressed to produce either stone from dry vapour or metals from wet. The second centred on the dual pro- cesses of liquefaction and solidification driven by exposure to heat or cold. Compounds of earth and water were particularly susceptible to these forces. When heat drew out the moisture these would become more densely packed. Cold might equally create something more solid by driving off heat and with it evaporated moisture. Aristotle differentiated between a material cause – proportions of water and earth present in a particular body – and an efficient cause, the application of heat and cold. The ratio of earth to water in combination with full or partial removal of moisture by heat and cold accounted for the great variety of stones and metals. In the latter water con- tinued to predominate, in the former earth.

The earliest extant Islamic systematisation of the creation of metals and stones is found in epistle 19 of the Brethren of Purity dating to the tenth century (Levey, 1967). Elements of Aristotelian thought can be clearly identified. But the thoughts of the Brethren were more influenced by the idea, first developed by the eighth-century alchemist Jaber ben Hayyan (known in the west as Geber to whom many hundreds of alchemical texts were later ascribed), that all metals were made from compounds of mercury and sulphur. Thus, various moistures in earth buried in caverns, they argued, were dissolved by vapours caused by heat. The moistures evapor- ated, rising to the top of caves where they cooled and coagulated, became viscous and ran down the sides of the cave where they mixed with dust and clay. This liquid amalgam then collected at the bottom of the cave where it was simmered by heat to become purified, heavy and thick. This produced mercury. Where additionally oily and airy particles became incorporated

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into the mix, the result was sulphur. What subsequently happened was dependent on a number of external and internal factors. Where sulphur dried out the mercury through the action of heat so that no further cold or dryness was gathered, this produced gold. If affected by cold after they had united this gave silver or by dryness then red copper. Fluctuations in temperature and initial composition before union produced other things. Cold resulted in hardening to tin-lead. If they

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met cold before they were refined and dust was present in large quantities this produced black iron. If there was more mercury than sulphur and less heat this would create black lead, but if heat was excessive the result was antimony. Marrying Aristotle and ben Hayyan, they concluded:

. . . the mineral obtained depends on the relative quantities and the varied conditions, whether sulphur or mercury is in excess or is light, or the heat is too strong or weak, or the minerals become cold before maturation, or they lose their proper weights. This is true of all minerals [i.e. metals] which may be melted.

(Levey, 1967: 15–19) The origins of stony materials such as crystal, hyacinth, chrysolite and

carnelian were thought to be different. These the Brethren considered to derive from rainwater and sediment (although no dust and clay in these instances) that could not escape from the cave due to its relative purity, weight and viscosity and which under heat was hardened into stone. Earthy minerals also began as mixes of water and earth that were subsequently fused by heat. If the earth contained saltpetre or salt it produced natron (a kind of soda ash) and alum (probably a kind of iron sulphate); if acidic, it produced green and yellow glass and calcite, and if the water passed through pebbles and sand it would create gypsum. Environmental conditions thus played an important part in what would be created as did the time it took for the process to reach full maturity. Sulphurs, salts, alums and vitriols (metal sulphates) were pro- duced in those places where dust, clay or salt predominated and were produced quickly in less than a year. In contrast gold, silver, copper and iron were usually formed within cavities in mountains and inside other rocks and took many years to complete. Hyacinth, chrysolite, opal, onyx, ruby, turquoise and diamond, produced under the same conditions, took many decades or even centuries to be created. Differences of colour stemmed from the influ- ence of the planets: golds and yellows were solar in origin, whites lunar. This spectrum would later be extended: blacks ascribed to Saturn, reds to Mars, greens to Jupiter, and blues to Venus.

Writing a century later Avicenna’s position on the formation of stones was very broadly Aristotelian in conception (Holmyard and Mandeville, 1974).

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Stones, he stated, were created either through the hardening of clays under the influence of the sun (clays that were naturally sticky were more likely to undergo conversion to solid stone than those that were dry which would simply crumble) or through the congelation of water in interaction with a mineralising or earthy force. Aqueous stone either formed from water drop- lets (here Avicenna was presumably thinking of the formation of stalagmites and stalactites or something similar) or through the petrifaction of deposits

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adhering to river beds. Both of these metamorphoses from liquid to solid were prompted by the earthy drying force found in the ground into which the water came into contact or again through the influence of heat. Just as heating and drying lay behind the formation of stones, cold and moisture were potential corrosive powers that could lead to their disintegration and erosion.

Towards the end of his life, al-Birunc provided the Islamic world with its most extensive treatment of stones, minerals and metals, The Sum of Knowledge about Precious Stones. He too followed the theory of the vapours and advoc- ated the union of mercury and sulphur as the cause of metals. Together Aristotle, often through the filter of Averroes, ben-Hayyan, the Brethren of Purity, Avicenna, and al-Birunc provided the middle ages with its most coherent account for the natural process implicated in the formation of stones and metals. Their impact on thinking beyond the Arabic world is reflected in the total reliance that Gershon ben Shlomah placed upon their works in his encyclopaedia. And they were also heavily drawn upon when the first original work on mineralogy in the Latin west, Albertus Magnus’ De mineralibus (On Minerals) was written some time before 1280 (Wyckoff, 1967). On stones Albertus followed the usual authorities, but in the field of metallurgy his contribution was more original because of his methodology. In the first instance, Albertus visited the mines in the Erzgebirge and exam- ined the metal-bearing veins at close quarters [Doc. 29]. By using miners’ testimony alongside what by the later thirteenth century was a vast corpus of alchemical literature, he produced a work that went beyond natural philo- sophy and anticipated the scientific method (Riddle and Mulholland, 1980).

But it was an earlier work that was truly remarkable for its precocity and which stands out as one of the greatest contributions to the advancement of the natural sciences made during this middle ages. If Avicenna had followed Aristotle on the formation of stones, what he said about large-scale geological processes belonged to him alone. His theory of superimposition and sedi- mentation, when linked to explanations for uplift – the two processes which

he rightly identified as responsible for why fossils should be found in strata high up mountains – pre-empts the final acceptance of these principles in the west by approximately eight hundred years:

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It is possible that each time the land was exposed by the ebbing of the sea

a layer was left, since we see that some mountains appear to have been piled up layer by layer, and it is therefore likely that the clay from which they were formed was itself at one time arranged in layers. One layer was formed first, then, at a different period, a further layer was formed and piled [upon the first, and so on]. Over each layer there spread a substance of different material, which formed a partition between it and the next

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layer; but when petrification took place something occurred to the parti- tion which caused it to break up and disintegrate between the layers.

As to the bottom of the sea, its clay is either sedimentary or primaeval, the latter not being sedimentary. It is probable that the sedimentary clay was formed by the disintegration of the strata of mountains.’

(Holmyard and Mandeville, 1974: 620)

Pedology: The science of

In the area of pedology other real and substantive advances were made

soils.

during the middle ages. Agronomists of antiquity had used a very restricted range of criteria to characterise soils. In essence they were interested in their elemental qualities – whether a particular soil was hot or cold, wet or dry. Agricultural activities such as fallowing, manuring and crop rotation were all designed to balance levels of temperature and humidity. Those soils that were naturally or through intervention in equilibrium were deemed good, those that remained in a state of imbalance were poor. Consequently soils were often described in terms of very simple oppositions: a soil might be heavy or light, smooth or lumpy, wet or dry. Medieval farming methods certainly continued to use this framework and it is the case that when medi- eval agronomists such as Walter of Henley or Pietro di Crescenti in the Latin west or Ibn Al-Awwam in Moslem Spain wrote about soils they did so under the influence of elemental theory (Oschinsky, 1971; Clément-Mullet, 2000). But more generally, the medieval sources also reveal a growing descriptive vocabulary. Over and above the classical criteria, additional emphasis was placed on new aspects of the soil – their colour, texture, taste, smell – deter- mined through the use of all the human sensory powers. Thus soils were described as sandy, clayey, muddy, ashy and burnt; malleable, limp, greasy and slippy; fat, thick, compact, dense and porous; honest, sweet, fresh, sour and bitter (Bolens, 1975). These terms were born in the fields not in the folios of learned texts. They came from experience of the soil rather than the thoughts of earlier agronomists. Nor was it confined to a particular cultural context. It might be expected that farmers operating in more northern latitudes would find the Graeco-Roman agricultural corpus, transmitted to the middle ages through compilations such as Geoponika, wanting since this tended to deal exclusively with Mediterranean climes. But even in Moslem Spain this descriptive revolution was also played out.

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All of this may seem rather inconsequential, a shift in terminological preference and nothing more. In fact what it reveals is deeply significant. It shows that those who were not bound to the conventions of the Classical canon were much freer to develop alternative methods of classification that had no precedent. If medieval scholarship was conventionally derivat- ive, the same charge could not be ranged against the unread. It was beyond the written word that brand new ways of thinking about and conceptualising

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nature were developing during the middle ages. Farmers not scholars were the real innovative thinkers of the age. It was the anonymous masses who were as much responsible for ushering in the scientific age as the celebrated names whose works have been trawled for evidence of its beginnings. For it was out of this seemingly disorganised mass of distinguishing soil markers, as much as the work of Avicenna, that the detailed disaggregating scientific classifications of later ages would evolve.

Further reading

Accessible texts of English lapidaries can be found in Evans and Serjeantson, English Mediaeval Lapidaries. See also Riddle ‘Marbode of Rennes’ (1035–1123) ‘De lapidibus’. On medieval geology Riddle and Mulholland, ‘Albert on stones and minerals’ provides an excellent way in to the subject; so too the introduction to Wyckoff, Albertus Magnus, De Minerabilibus. Said, Al-Beruni’s Book of Minerology provides an Arabic perspective.

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