Industrial Minerals

Industrial Minerals Exploitation in Antiquity in the Aegean: the case of the elusive “earths”

SASAA, in collaboration with Glasgow University’s Dept. of Archaeology, is involved in the identification and characterisation of “earths”, namely a select group of industrial minerals renowned in antiquity for the wide range of applications as medicines, pigments, cleansing agents or mordants. The means by which these materials were extracted and processed has been, until recently, conjectural, despite their fundamental importance in the everyday lives of the people of antiquity. 

In the course of this research project (*) a multidisciplinary approach has been undertaken to re-examine the documentary and archaeological evidence combined with extensive geological prospection regarding these most elusive of industrial minerals of antiquity, the Lemnian and Samian earths. They were famed in Classical/Roman and the Ottoman periods primarily for their healing properties as well as a wide range of other applications, as fuller’s earth, pigments and clays for pottery-making. 

Lemnian earth, venerated by the 2nd-c BC doctor Galen, and seen below stamped by the priestess “in charge” of its extraction, was famed in Classical/Roman and also Ottoman times as an antidote to snake bites and against plague.


The annual “sealed earth” ceremony at Lemnos

(From an oil painting of RA Thom; by permission of the estate of RHS Robertson 1986, 37)

Despite extensive documentation, the Lemnian sphragis (seal) and the two types of Samian earth, the colyrium and the aster, have remained distinctly elusive in the archaeological record. The reason is that as raw materials, products and industrial waste they are readily assimilated into the background of the natural environment. Not only are they elusive in the field but the main ingredients to which they owed their curative properties have not been identified either. This joint research program between Glasgow and Athens, part of a larger program into the nature and methods of processing of other industrial minerals in the Aegean (**) has been aimed at identifying their mineralogy and potential locations of extraction on their respective islands as well as illuminating the nature of the main ingredient responsible for their curative properties.


Samian Earth: the case of “colyrium” and “aster”

Although documentary evidence of the exploitation of Samian earth dates from the time of Theophrastus in the 4th century BC it is Pliny in c. 50 AD (Nat. Hist.) who details two distinct varieties. These are “colyrium” an eye salve and “aster” which was used as a soap as well as in medicines. Samian earth is described as a white, soft lightweight substance, clearly a valuable versatile material, a typical industrial mineral.

The present search for Samian earth followed the suggestions of the Samiot geologist Karageorghiou (1947) and IGME geological maps, that the volcanic rocks in the vicinity of Platanos were the likely source.

SEM-SE image of texture of clay in bentonite, (sapounochoma) at high magnification (SAM47).

These rocks have been altered to a soft absorbent clay mineral known as fullers’ earth or bentonite. However, the medicinal value of this material is only limited, as an absorbent of toxic substances and it is likely that a second substance was present with more powerful medicinal and antiseptic properties. The existence of borate minerals, like collemanite identified in localities near Platanos point to the special substance being a soluble borate, well established ingredient in modern pharmaceutical products. Therefore it is suggested that Pliny’s colyrium contains borate as the active ingredient while aster was a clay used as fullers’ earth.


Hephaestias in Galen’s time, 167 AD

View of the Vouni-Kastro, the cone-shaped hill in the far distance, often identified as the legendary Mosychlos;

from the site of Hephaestias excavations of the Italian School of Archaeology at Hephaestias (1930’s to present).

It is Galen during his visit to Hephaisteias, in 167AD, who gives an insightful account of the method by which the Lemnian earth (LE) was extracted and processed (De Simpl. Med., xiii, 246-248). Its colour was clearly red since it was referred by some as “Lemnia miltos” but differed from this in not leaving a stain when handled (Galen in Brock 1929, 192). Galen was particularly curious to verify this last point. “I thought well to inquire whether there was no tradition of goat’s blood being mixed with the earth. All who heard this question of mine laughed, and they were not mere chance individuals, but people well informed about the whole history of the locality as well as in other matters” (Galen, in Brock 1929, 194).

Galen distinguished three varieties of LE: a) the first (the medicinal one) was handled by the priestess herself, the second, also red, was used by builders (presumably as a pigment), the third for the cleaning of wool and other garments (Galen, xiii, 247). Fuller’s earth is calcium montmorillonite or, in industrial minerals parlance, a bentonite with a vast range of applications in the modern world. Kimolian and Samian earths appear also to have been bentonitic clays.


Kotsinas in Belon’s time, 1543 AD

It was first on the Trojan war hero Philoctetes, that the priests of Hephaestus applied the LE, curing him of the unbearable stench and pain of his wound inflicted by the poisonous Hydra. Galen was so convinced of its effectiveness that he reports enthusiastically “I had no hesitation myself in testing the medicine, and I took away (back to Rome!) twenty thousand seals”.

Fourteen centuries later, in 1543, Belon, the intrepid 16th century traveller and natural historian, visited Constantinople where, after making enquiries, he encountered 18 types of different materials marketed as Lemnian Earth. It soon became apparent to him that some debasing was taking place. Therefore, he engraved the “brand name” of the real LE sphragis in his book for the benefit of the medical world.



Terra Sigillata (Lemnian Earth) in the process of being sealed

(from “Ortus Sanitas” c. 1550, Robertson 1986, 38).

More important perhaps from the modern researchers’ point of view, is Belon’s description of how to get to the extraction point, which, after visiting it, he says was near the ruins of Hephaestias. “From the corner of the castle (at Kotsinas) we walked towards the hill which is not more than four arrow-shots away. Between the port and the hill there is a small chapel called St Saviour’s, where the monks gather on the 6th of August, the date set for the extraction of the earth from its vein. After leaving the church and walking towards the hillock we found two paths, one to the left and one to the right leading to two springs, one about one arrow-shot away from the other” (Belon in T-S 1986, 79). Now Belon was no archaeologist and the ancient city of Hephaestias was not revealed until the late 19th century. Therefore he mistook the remains of the castle at Kotsinas with those of Hephaestias. He was, however, right about the two springs, the one which runs all year round, called Phtheleidia.

In the course of geological prospection, altered and weathered pyroclastic rock was observed in the crags about 20m NW of the spring. Some were intensely altered showing colours from white to yellow and brown to red. X– ray diffraction analyses showed that clay minerals like montmorillonite and illite were the main components with cristoballite, relict feldspar, quartz and alunite. Alunite, a potassium aluminium sulphate forming as the result of high temperature alteration of feldspathic volcanic rocks, is usually associated with alum and sulphur. Alum, aluminium sulphate, was well known in antiquity for its medicinal properties but being particularly soluble, it would have been washed by rain out of the high volcanic ground into the alluvial sediment in the fields below or into man-made traps. The Dutchman Joos van Ghistele who visited Lemnos in 1485 reports on one such “trap”: (LE) is a pool which dries up every summer and is full of water in winter...a thick scum, variegated in colour, forms on its surface (Hasluck and Hasluck 1929).

It is concluded that the different “varieties” of LE earths with various textures (sticky, greasy and granular) and colours which are referred to by Galen are products of the same hydrothermal alteration around the Phtheleidia spring. In some types of rock the alunite predominates, in others the clay minerals, leading to its different properties and applications.

SEM-SE image of fragment of red altered volcanic rock from the track to the Phtheleidia spring.

Rich in sulphur, presumably alunite, it suggests of the potential presence of alum.



AJH examining altered sediments in wall of entrance to probable early
sulphur mine, Melos, Greece (SE Melos survey).


Further information

Industrial minerals in the Aegean website

Lemnian Earth publication by Potigaire Press




Belon P, 1553, Les Observations sur Plusieurs Singularités…, Paris.

Brock A J, 1929, Greek Medicine, J M Dent and Sons.

Hasluck F W and Husluck M M, 1929, Christianity and Islam under the Sultans, Vol. 2, Ch. LII, Terra Limnia, 671-688, Oxford.

Karageorgiou E D, 1947, Samos (on geology, minerals, etc.), in Zafiriou 1946-62, 2, 212-24.

Messineo G, 1993, Annuario della Scuola Archeologica di Atene, Vol. LXVI-LXVII, Roma.

Tourptsoglou-Stefanidou V, 1986, Taxiodiotika ke Geograhica kemena ya tin neson Lemno (15o-20o aeonas) (Geographic and Travellers accounts about the island of Lemnos (15th-20th centuries), University of Salonika, The Polytechnic School, Vol. 8, Annex 33, 660 pp.



Authors: E Photos-Jones 1, 2, A J Hall 1, V Perdikatsis 3, S Chiotis 3 and E Demou3.


1 Department of Archaeology, University of Glasgow, Glasgow,

2 Scottish Analytical Services for Art and Archaeology, Glasgow,

3 Institute of Geology and Mineral Exploration, Athens.


(*) The authors are grateful to the British Council and the Greek General Secretariat for Research and Technology for the funding of this project. Also M Malamos, GUAD, for documentary research and S D’Alessandro-Rodger, SASAA, for the preparation of this leaflet. For a full report see by the same authors, “Industrial Minerals Exploitation in the Aegean: the case of Samian earth”, unpublished SASAA13.2A/GUAD, pp. 24, Glasgow, June 2000 “Industrial Minerals Exploitation in the Aegean: the case of Lemnian earth”, unpublished SASAA13.2B/GUAD pp. 52, Glasgow, June 2000. (**)GUAD, as a member of the British School at Athens is currently carrying our research on industrial minerals in Antiquity in Melos (Melian and Kimolian earths, alum and sulphur).