Fig. 1: Four jadeitite tools, and a sawn piece of the raw material (from the Alpine locality of Monte Viso). These tools were especially curious for archaeologists in that a) they seem perfect, unused, and b) they are made of a rare rock type unknown in the regions where they were found, and unknown across the whole of Ireland. Tracing the source of an artefact, or the material from which it was made, is known as a provenance study, and can give archaeologists evidence of trade routes and social patterns in Antiquity. Jadeite, the essential ingredient of the rock jadeitite, is an uncommon sodium-rich pyroxene. It is the staple of valuable Burmese jade --- many other jades are known as nephrite, the main constituent of which is an amphibole, a silicate family closely related to the pyroxenes. Specimens on display at the Irish National Museum of Archaeology, in downtown Dublin, photographed in September 2019. They were found in counties Mayo, Donegal and Westmeath, and are all Neolithic, dated at 4000-3800 B.C.
Figs. 2-3: Close-ups of two of the fine tools. Specimens on display at the Irish National Museum of Archaeology, in downtown Dublin, photographed in September 2019. The item on the left (1880:97) is from Kincraigy in county Donegal. That on the right (1901:42) is figured in the museum booklet (Kelly, 2007, p.9): it was found at Paslickstown in county Westmeath.
"Rock of the Month # 224, posted for February 2020" ---
There are some interesting stone tools on display at the National Museum. In particular, there is a set of 4 jadeitite axes, finely crafted and unworn, suggesting ceremonial use. Their colours, craftwork and material distinguish them from some 21,000 other Irish axe heads made of varied raw materials that are native to Ireland. A provenance study determined that the jadeitite raw material was not Irish, but from northern Italy, circa 4000-3800 B.C. The rare finds came from counties Mayo, Donegal and Westmeath. Other stone tools of less exotic materials are made from porphyry, porcellanite, chert / flint and assorted other Irish rocks, of mixed volcanic and sedimentary origins.
Northern Italy is known to preserve some rocks subjected to intense metamorphism at shallow mantle depths. These include magnesian metapelites (sediments rich in clay minerals, originally deposited as shale or mudstone), subducted to depths of about 100 km in the mantle within the last 100 million years, and returned to the surface. Such rocks are described from the Dora Maira massif. They include fine- and coarse-grained pyrope (garnet) quartzites and Na,Fe-rich jadeite-kyanite quartz layers (Tilton et al., 1989). Such intense metamorphism could have turned graphite (if present) into diamond.
Some of these metamorphic rocks are very hard, and thus prospective raw material for stone tools. Prehistoric use of eclogites and jades indicates that early Europeans agreed! Neolithic Age stone tools are very abundant in northern Italy and southeast France. Their mineralogy and textures are consistent with a provenance in the eclogitic rocks of the western Alps. Most common in the western Alps and foothills, the tools are also found, singly, up to 1,000-1,700 km away: in northern Scotland, Scandinavia, Sicily and elsewhere. Near the western Alps, eclogites prevail over jades, whereas further away the jades are dominant. The latter exhibit granoblastic and mylonitic textures (D'Amico et al., 1995).
Material from sources in northwest Italy traded widely across Europe in the 5th and 4th millennia. The rock types include eclogite, omphacitite, jadeitite and amphibolite. Different raw materials appear in different regions, e.g., dark rocks in north italy and southern France, lighter material of the jadeitite family appear in the Paris basin, in Germany and in the UK and Ireland (Pétrequin et al., 2011). Anne-Marie and Pierre Pétrequin and colleagues devoted projet JADE (2006-2010) and the follow-up JADE 2 to long axeheads of Alpine jade which were circulated around all Europe in the 5th and 4th millennia B.C., from the Mediterranean to the North Sea coasts, and from ther Atlantic to the Black Sea. Their reports consider more than a century of petrographic studies in light of the archaeological context of an expanding database of specimens of large stone axes. A novelty of their expanding database is the consistent application of the technique of spectroradiometry, the non-destructive collection of reflectance spectra from each object.
The prehistoric jade sources were 1) Monte Viso (Monviso, elevation 3,841 metres, in the Cottian Alps which continue southwestwards into France as the Queyras Mountains, to the northwest of the Maritime Alps and southeast of the Massif du Pelvoux in the national park of the Ecrins) in the Piedmont, near the modern French border, 65 km southwest of Turin (Pétrequin et al., 2011, pp.66-67) and, just 100 km away, 2) the Beigua massif northwest of Genoa, in the coastal province of Liguria. Seasonal mining and working of the chosen rock types occurred at sites 1500-2400 metres above sea level. The jades travelled as far as 1700 straight-line km from source, and their nature speaks to practices in markedly inegalitarian societies (Pétrequin et al., 2015). The jade quarries on Monte Viso were exploited mainly in the period 5000-3700 B.C. (ibid., p.86). Imitations of the axe heads made from Alpine rocks were eventually made of local rocks, such as flint.
D'Amico,C, Campana,R, Felice,G and Ghedini,M (1995) Eclogites and jades as prehistoric implements in Europe: a case of petrology applied to cultural heritage. Eur.J.Mineral. 7, 29-41.
Kelly,EP (2007) Guide to the National Museum of Ireland: Archaeology. National Museum of Ireland, Dublin, 48pp.
Pétrequin,P, Sheridan,A, Cassen,S, Errera,M, Gauthier,E, Klassen,L, le Maux,N, Pailler,Y, Pétrequin,A-M and Rossy,M (2011) Eclogite or jadeitite: the two colours involved in the transfer of alpine axeheads in western Europe. In "Stone Axe Studies III" (Davis,V and Edmonds,M editors), Oxbow Books, 55-82.
Pétrequin,P, Sheridan,A, Gauthier,E, Cassen,S, Errera,M and Klassen,L (2015) Projet JADE 2. `Object-signs' and social interpretations of Alpine jade axeheads in the European Neolithic: theory and methodology. In "Connecting Networks" (Kerig,T and Shennan,S editors), EUROVOL Workshop on Lithic Exchange, 83-102.
Tilton,GR, Schreyer,W and Schertl,H-P (1989) Pb-Sr-Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira Massif, Western Alps, Italy. Geochim. Cosmochim. Acta 53, 1391-1400.
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See an earlier article, and references therein, on jade in China.