This month’s blog from our Community Geologist, Dr Ian Kille, is all about the Romans and mining…
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It was like walking in snow, except that we were surrounded by leafy trees in bright summer sunshine and 20 degrees of heat. The creamy white crystals that were reflecting so much light were not the pretty hexagons of ice-crystals but the rhombohedra of calcite. The drift of material we were intent on searching stuck out like a huge tongue between the wooded hillsides, pointing towards the wonderfully named village of Snailbeach in Shropshire. Lichens and moss, mares-tails, stonecrop, cinquefoil, willowherb and even small trees were starting to colonise the bottom edges of the mound where more water collected. Despite this and the surrounding borderland idyll the mine waste maintained a zone of lifeless desolation even 20 years after the mine’s closure in 1955. For my geo-pal Kevin and I, though, it was a world of excitement. We were here on a cycling holiday, or rather a collecting trip which involved some cycling and camping. Along with hunting for trilobites in the county’s famous Silurian and Ordovician outcrops, we were exploring the lead and zinc mining industry of Shropshire to see what beautiful specimens we could find in the disused mine-tips. We were also teenagers, away from home and relishing the freedom that this gave.
In amongst these old tips, it was still possible to find some fine specimens. Along with the brilliant crystals of quartz and the milky crystals of calcite, there were deep brown crystals of sphalerite. Sphalerite (zinc sulphide) is one of the main ores of zinc and valuable in its own right, as zinc is used as an alloy with lead to make solder and with copper to make brass. The name sphalerite and its alternative, blende or zinc blende both refer to sphalerite’s similarities with another ore mineral, galena. To Kevin and I galena was the prize, it felt fabulously dense in the hand and formed beautiful octagonal and cubic crystals which glittered in seductive greys. Galena (lead sulphide) is the principal ore of lead and for early miners sphalerite was a distraction from this valuable lead ore. The name sphalerite come from the Greek word Sphaleros meaning treacherous and Blende come from the German word Blenden to deceive. Clearly the word-coining miners were not happy about Zinc Sulphide.
It is curious that the Romans, who knew about zinc and its use in making brass, don’t appear to have mined the copious amount of zinc available in deposits in Britain. They did however know about the lead and mined large quantities of it exporting it all over the Roman Empire. It seems likely that lead (along with iron, tin, copper and gold) is what drew the Romans to Britain and encouraged them to make it part of the Roman empire. Lead mining started soon after the invasion of Britain with evidence of workings at Charterhouse in the Mendips as early as 49AD. This became a highly organised and productive set of open cast workings which by 70AD had overtaken the lead-mines of Iberia as the principal source of lead for the Empire. There is also a good fictional account of this mine in Lindsey Davis’ book “The Silver Pigs” which gives a real sense of the conditions in which mining took place along with some enjoyable speculations on the political and economic intrigue that may have surrounded such a valuable resource.
Lead is not only very dense but is malleable, durable and waterproof. The Romans understood this, and it was used principally to make pipes to carry water and for lining aqueducts, and also to make pewter plates and coinage. Galena itself (along with stibnite, an ore of antimony) was crushed to a fine paste to make khol which was used as an eye cosmetic. Some Romans also understood that lead was not good for their health. Vetruvius wrote in the 1st century BCE: “Water conducted through earthen pipes is more wholesome than that through lead; indeed that conveyed in lead must be injurious… This may be verified by observing the workers in lead, who are of a pallid colour; for in casting lead, the fumes from it fixing on the different members, and daily burning them, destroy the vigour of the blood; water should therefore on no account be conducted in leaden pipes if we are desirous that it should be wholesome.” (VIII.6.10-11)
Pliny on the other hand, writing in the 1st Century CE, noted that “Fresh hogs’ lard, applied as a pessary, imparts nutriment to the infant in the womb, and prevents abortion. Mixed with white lead or litharge, it restores scars to their natural colour” (Book 28: Remedies). He also advocates that lead could be used as a liniment, or as an ingredient in plasters for ulcers and the eyes, among other health applications. As an aside this underscores that Pliny’s Natural History along with useful direct observation has a great deal that is unverified anecdote. For example: “Sneezing, provoked by a feather, relieves heaviness in the head; it is said too, that to touch the nostrils of a mule with the lips, will arrest sneezing and hiccup” (Book 28: Remedies, Chapter 15), and “For patients affected with melancholy, calves’ dung, boiled in wine, is a very useful remedy.” (Book 28: Remedies, Chapter 67). Taking this into consideration, his common appellation as a scientist does the meaning of science no favours. On the other hand, his detailed records of methods used in mining, extracting and refining metals are valuable resources in understanding what the Romans were making and how they did it.
Pliny gives detailed descriptions of the way that lead is extracted from its ore, galena. From this and other sources we know that lead, despite its value, was a by-product. Galena commonly contains a small fraction of silver, up to 0.5%, making silver the ore’s most valuable component. In writing this article I found a derivation for galena as “From Latin galena – “dross from smelting lead”” – it is a nice idea which I have been unable to verify.
For the Romans silver was not only used for high status ornaments and tableware but was the fundamental currency for the empire. We know from Pliny that the process used to extract the silver was cupellation. Lead melts at a relatively low temperature (327oC ) whereas silver melts at 960oC. When heated to circa 1000oC lead will oxidise to form litharge (PbO) which can be absorbed into a porous calcareous material such as bone ash, leaving the now molten silver fraction. Typically, the bone ash was formed into a truncated cone shaped vessel; a cupel. The litharge having been absorbed would leave drops of silver at the base of the cupel. Later, the lead would be recovered from the cupel by re-smelting and the lead would be formed into an ingot, or pig, each weighing approximately 69kg.
The Romans’ quest for silver and lead in Britain was not confined to the Mendips. Roman lead mining has been identified in Wharfedale and not far from Hadrian’s Wall at Alston Moor. A Roman pig of lead was also discovered not far from the mine at Snailbeach making it another likely location for Roman lead/silver mining and extraction. All of this I neither knew nor cared about on my teenage visit, I was simply happy to have found some beautiful mineral specimens. Mystery rock number 19 for the Hadrian’s Wall Archaeology Project is one of the specimens that came back from that trip… and finding it would have been a good reason to head, once more, to the Stiperstones Inn.
Attributions and References
References:
Roman Lead Working in Britain. R F Tylecote (1964). British Journal for the History of Science vol.2 no.5.
Attributions:
Shropshire view: from http://www.shropshiresgreatoutdoors.co.uk/site/snailbeach-mine/
Galena: Galena with some golden colored pyrite (3.5 × 2.5 × 2.0 cm) from Huanzala mine, Huallanca, Bolognesi, Ancash, Peru. Ivar Leidus, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons.
Lead pipe: By <a href="https://en.wikipedia.org/wiki/User:Solipsist" class="extiw" title="en:User:Solipsist">Andrew Dunn</a> – <span class="int-own-work">Self-photographed</span>, <a href=”https://creativecommons.org/licenses/by-sa/2.0″ title=”Creative Commons Attribution-Share Alike 2.0″>CC BY-SA 2.0</a>, <a href=”https://commons.wikimedia.org/w/index.php?curid=606468″>Link</a>
Lead Pig: British Museum. https://www.britishmuseum.org/collection/object/H_1856-0626-1
Sciapod from Pliny’s Historia Naturalae: By Michel Wolgemut, Wilhelm Pleydenwurff (Text: Hartmann Schedel) – http://www.beloit.edu/~nurember/book/images/Miscellaneous/, Public Domain, https://commons.wikimedia.org/w/index.php?curid=490581