Travels of an Urban Geologist: Building Bavaria II

The pretty, Medieval town of Nördlingen lies, fittingly, on the ‘Romantic Road’ in the west-central Swabian Bavaria. Its red-roofed buildings are enclosed within a complete and circular circuit of town walls. This is best viewed, along with the surrounding, rolling green countryside from the 90 m high tower, ‘The Daniel’ which is built over the west entrance of the town’s main church.

St Georg’s Church sits in the centre of Nördlingen, was built in the second half of the 15th Century. The tower was finally completed in 1639 and, because of the splendid views, it is named after a text from the Book of Daniel; “Then the king made Daniel and […] made him ruler over all the land” (2.48). The grey, breccia used to build the church came from the nearby quarry at Altenbürg, and is generally known as Bavarian Trass. ‘Trass’ generally refers to volcanic derived rocks which form a pozzolanic additive when mixed with lime cement, producing an hydraulic set and in indeed the trass from Nördlingen was also used for this purpose.

IMG_2018 IMG_1914Above left, St Georg’s Nördlingen and Right, Altenburg Quarry

But this is no ordinary, volcanic-derived Trass, such as those quarried in the nearby Rhine Graben. The Bavarian Trass of Nördlingen was formed by a meteorite impact.

Nördlingen lies in the Ries impact crater, created 14.5 million years ago (in the middle Miocene) from the impact of a meteorite. The crater is 24 km in diameter, and the bolide hit a target of Mesozoic limestones, up to 800 m thick which had been deposited on top of Hercynian basement rocks, granitoids, gneisses and amphibolites. At impact, the bolide was vapourised, the extremely high pressures exerted caused melting in the target rocks and of course an explosion, which threw molten rock, molten bolide and rock fragments upwards and outwards, this mix fell back down to Earth into the crater and surrounding areas. Impact melt breccias form a specific and distinctive rock type known as suevite, named after Suevia, the Latin for Swabia. The Ries Suevite has a grey, glass-rich, tuff-like matrix supporting angular clasts of basement derived granite and gneiss, keuper clay, sandstone, Malm limestone and slugs of glass. The latter where incorporated into the breccia whilst still semi-molten and these distinctive textures are known as ’Flädle’.


ries-sectionA map and cross section of the Ries Impact Crater after Osinski (2004), showing the distribution of suevites in black.

IMG_1983 IMG_1952Above left; suevite in a quarry exposure, with coasts of granite and black Flädle. Right Flädle are obvious in the ashlars used in the church walls.

Visitors to Bavaria may well have eaten the delicious Flädlessuppe, which contains noodle-like strips of pancake, the Flädle. The variety found in suevite are somewhat less digestable, and as glass they contain molten components of both the target rocks and the vaporised bolide.

IMG_2009 IMG_2010Above, suevite used as building stone in the Daniel, with clasts of gneiss, limestone and Flädle.

Bavarian Trass, or Ries suevite, is probably one of the world’s most unique building stones. Though many would like to claim so, few churches have been built with an extra-terrestrial contribution.

References and further reading …

Osinski, G. R., 2004, Impact melt rocks from the Ries structure, Germany: an origin as impact melt flows? Earth and Planetary Science Letters 226, 529– 543.

Ries Geopark:

Posted in Building, Building Stone, Geology, Germany, Impact, Meteorites, Ries | Tagged , , , , , , | Leave a comment

Travels of an Urban Geologist: Building Bavaria

IMG_3810Bavaria is a huge province of modern Germany. Recently I visited the southern parts, the Allgäu and Upper Bavaria regions, out on the Molasse Basin of the northern Alpine Foreland, staying in the town of Memmingen. The countryside looks like a picture-book, full of toy farms with green manicured grasslands spotted with white, plastered houses with red tile roofs (right). What is noticeable is there is less of the slate and stone seen in the French and Italian Alpine forelands. However in the few towns and villages I visited, churches and modern shop fronts featured stone masonry or cladding. The building stones used were striking in being predominantly fairly recent looking breccias and tufas. I just assumed they were from the Molasse. I pointed one out to my (non-geological) friends and Amira, a local, immediately said ‘my Dad will know exactly what this is’. Amira’s Dad did know, he told us it was ‘Biberstein’ and it was related to the Ice Ages. Dads always know these things. So I started to look into this a little bit more.

Now, I have spent many years studying and teaching Alpine Geology, but have pretty much managed to ignore the Ice Age geology of the region. Somewhere deep I recall the mantra of Günz, Mindel, Riss and Würm, the original glacial periods devised by Alpine geomorphologists and geologists at the turn of the 19th Century. During the glaciations which define the Pleistocene Stage of the Quaternary, the Alps were covered by a huge ice cap, with enormous glaciers descending towards the southern and northern forelands. In Upper Bavaria, large lobate piedmont glaciers coalesced to form the Inn-Chiemsee Glacier, which was at its greatest extent during the last glacial maximum around 21 thousand years ago (ka). This ice body excavated the famous moraine field around the town of Rosenheim and when it retreated, left behind the enormous glacial Lake Rosenheim, the remnants of which are the present day Simsee and Chiemsee. However this was the last of at least four major glaciations, the Würm. The Victorian glacial chronology has been considerably refined over the last century, but the terminology remains essentially the same. The four main glaciations, Günz, Mindel, Riss and Würm each lasted around 100 thousand years, separated by warm periods of similar lengths.

IMG_3820Glacial Lake Chiemsee, with the Bavarian Alps behind

Quaternary deposits from the Bavarian-Austrian Alpine foreland have been used as building materials since the Roman period. The most famous and most widely used are the Brannenburg Nagelfluh, the Hötting Breccia and the calcareous tufa deposits worked between the Inn Valley and Vorarlberg. A major advantage of these stones, compared with the bedrock of the Alpine series, is that they are soft and easy to quarry, hardening on surface exposure. Despite their young geological age, these Quaternary deposits have been surprisingly resilient to weathering and erosion. They often display large porosity, which, far from being detrimental, has contributed to the resistance to decay; the stones dry out more quickly rather than preserving water in small pore spaces. Having formed at the Earth’s surface and not having undergone major periods of burial or diagenesis, they are at ‘equilibrium with their environment’ (Mirwald et al., 2012). They have been use since at least the Roman period, and some still continue to be quarried today.

A locally sourced and much used stone is the wonderfully named Brannenburger Nagelfluh from Brannenburg am Inn, in the Inn Valley of Southern Bavaria, south of the town of Rosenheim. This is Amira’s father’s ‘Biberstein’ named from the Biber hill near the quarries, and Biberstein is the colloquial name for this stone. The word ‘Nagelfluh’ is used in the German geological literature to refer to young (Tertiary or Quaternary) formations of conglomerate. Nagel means nail, and the name refers to the fact that in outcrop, the rock surface appears to have large nails hammered into it, so that only the heads are seen. Brannenburger Nagelfluh is a (just) coast supported, polymict conglomerate with a ratio of clasts:matrix of 50:50. The clasts are moderately sorted, up to around 10 cm across and composed of a variety of rock types derived from the Alps; limestone, sandstone, gneiss, amphibolite schist, dolerite and quartz. Brannenburger Nagelfluh formed on the shores of the Rissian Lake Rosenheim, and they represent a series of deltaic deposits, which are exposed in the quarries around Brannenburg and Flintsbach (Herz et al., 2014). These sediments were deposited at around 150 ka. The topsets are exposed in the Anton Huber Quarry and foresets are exposed in the Grad Nagelfluhwerk quarry. Grey and yellow varieties are observed in photographs of the quarries published in Herz et al. (2014).

IMG_3586 IMG_3590 Above: Shop fronts in Memmingen

IMG_3929 IMG_3910Brannenburger Nagelfluh used in Ludwig II’s crazy fountains at Schloss Herrenchiemsee

A superficially similar stone is the Hötting Breccia. This is an alluvial fan and talus slope deposit, developed on the Northern Calcareous Alps basement. The breccias outcrop around Innsbruck, and are dated between 100-70 ka (Spötl & Mangini, 2006). They are therefore associated with the Riss-Würm interglacial period. Petrologically, they are carbonate-cemented breccias, with poorly-sorted clasts of the underlying Triassic limestones. Local concentrations of red Permian sandstones (Alpiner Buntsandstein) stain the lowest deposits of the Hötting Breccia yellow and red. These are up to 40 m in thickness. The overlying White Hötting Breccia does not contain Buntsandstein, and has only limestone clasts, however this was less well consolidated and was not used for building (Unterwurzacher et al., 2010). Several quarries operated near Innsbruck until the early 20th Century, the largest of which was Mayr (below). Transportation both north and south along the river Inn was favourable in the distribution of this stone and it is the main building stone in Innsbruck, where it was used for the Cathedral and other examples of civic architecture (Mirwald, 2012, Unterwurzacher et al., 2010).


Many modern buildings are clad with a grey matrix-supported breccia. We need to travel to the southern Alpine foreland to source this stone. This is ‘Ceppo’ from the shores of Lago di Iseo in the Italian Lake District. The Ceppo di Poltragno Conglomerate is a grey, carbonate-cemented breccia. Quarries are located in the Adda and Brembo valleys (Vola et al., 2009). Ceppo is a Quaternary fluvial-glacial conglomerate. It was deposited during the lower to middle Pleistocene (1.8 – 0.125 Ma) as diamictites and colluvial scree deposits. The clasts are matrix supported and are derived from the Triassic dolomites in the Carnic Alps (Forcella et al., 2012).

IMG_3569 IMG_3570 Above: Cladding on the ground floor of an office building in Memmingen

Ceppo has been quarried since the Roman period and is actively quarried today, used as cladding and as paving. Vola et al. (2009) have described its use in Bergamo and Bugini & Folli (2008) have described its use in Milan. Varieties known as Ceppo Gentile, Ceppo Gré and Ceppo Poltragno are marketed. Vola et al., (2009) list the following quarries; Camerata Cornello, San Pellegrino and Brembate Sotto (inactive) and Poltragno, Pianico, Grè (at Solto Collina on the lake shore) and Castro (active). The stone is exported throughout southern and central Europe and is widely used in southern Germany.

Back in Austria and Bavaria, tufa limestone occurs commonly across the Northern Calcareous Alps, found in association with cool spring activity, where waters are supersaturated with calcium carbonate. Important quarry sites are at Thiersee, in the Inn Valley south of Brannenburg and at Andelsbuch in the Vorarlberg of westernmost Austria. It could be relatively easily exported to the Allgäu region of Bavaria (Kempten and Memmingen) from this latter locality, along the River Iller. The stone is both strong and light in weight. Like many tufas and also large porosity stones such as the Portland Roach and the Florida Coquina, these stones are extremely effective in the constructions of fortifications as their properties allow them to absorb impacts (of cannon balls etc.) well. Thiersee Tufa was used to construct the Kufstein Fort in the Tirol (Mirwald et al., 2012). However there is good evidence that these stones have been won since the Roman period; they are used in the villa at Rankweil in the Vorarlberg (see Unterwurzacher et al., 2010). It is probably Andelsbuch Tufa that is used in the church at Memmingen (below).

IMG_3613 IMG_3609

At Thiersee, the tufa deposits are up to 10 metres thick and extended laterally, prior to quarrying for several hundred metres. They are primarily ‘moss tufas’ (Unterwurzacher et al., 2010). These deposits are no longer active and the deposits are almost worked out; peak production was in the 18th Century. At Andelsbuch, moss tufa and phytoclastic tufa have formed on top of the Helvetic Nappe and Flysch formations. The deposit is up to 5 metres thick and extends for 100 m. Tufa deposition here is still active (Unterwurzacher et al., 2010).

References and further reading

Bugini, R. & Folli, L., 2008, Piedras de la arquitectura milanesa (Stones used in Milanese architecture)., Materiales de Construcción, 58, (289-290), 33-50.

Ceppo di Gré:

Forcella, F., Bigoni, C., Bini, A, Ferliga, C., Ronchi, A., Rossi, S. et al., 2012, Note Illustrative della Carta Geologica d’Italia 1:50 000; 078 Breno., Servizio Geologica d’Italia., 313 pp.

Herz, M., Knipping, M. & Kroemer, E., 2014, The Rosenheim Basin: Würmian and Pre-Würmian deposits and the Höhenmoos interglacial (MIS 7). in: Kerschner, H., Krainer, K. & Spötl, C., From the foreland to the Central Alps: Field trips to selected sites of Quaternary research in the Tyrolean and Bavarian Alps., Excursion guide of the field trips of the DEUQUA Congress in Innsbruck, Austria, 24–29 September 2014., 6-17.

Huber Quarry:

Mirwald, P., Diekamp, A., Unterwurzacher, D. & Obojes, U., 2012, Weathering of sedimentary stone materials formed under Earth surface conditions., 11 pp.

Sanders, D. & Spötl, C., 2014, The Hötting Breccia – a Pleistocene key site near Innsbruck, Tyrol., in: Kerschner, H., Krainer, K. & Spötl, C., From the foreland to the Central Alps: Field trips to selected sites of Quaternary research in the Tyrolean and Bavarian Alps., Excursion guide of the field trips of the DEUQUA Congress in Innsbruck, Austria, 24–29 September 2014., 81-93.

Spötl, C., Mangini, A., 2006, U/Th age constraints on the absence of ice in the central Inn Valley (eastern Alp, Austria) during Marine Isotope Stages 5c to 5a. Quaternary Research, 66, 167-175.

Spötl, C., Starnberger, R. & Barrett, S., 2014, The Quaternary of Baumkirchen (central Inn Valley, Tyrol) and its surroundings., in: Kerschner, H., Krainer, K. & Spötl, C., From the foreland to the Central Alps: Field trips to selected sites of Quaternary research in the Tyrolean and Bavarian Alps., Excursion guide of the field trips of the DEUQUA Congress in Innsbruck, Austria, 24–29 September 2014., 68-80.

Unterwurzacher, D., Obojes, U., Hofer, R. & Mirwald, P., 2010, Petrophysical properties of selected Quaternary building stones in western Austria. In: Prikryl, R. & Török, A.; Natural Stone Resources for Monuments., Geological Society of London, Special Publication, 333, 143-152.

Vola, G., Fiora, L. & Alciati, L., 2009, Stones used in Bergamo architecture., Studia Universitatis Babe-Bolyai, Geologia, 2009, Special Issue, MAEGS – 16, 137-139.

©Ruth Siddall 2015

Posted in Alps, Building Stone, Geology, Germany, Quaternary | Tagged , , , , , , , , | Leave a comment

Catch a falling star: the strange story of the Tocopilla Meteorite

Think ‘meteorites’ and think ‘art’ and the average human mind will probably conjure up the garish and probably fantastical cover of a sci-fi novel depicting colliding worlds in shades of pink and blue or alternatively an ‘artist’s impression’ of the late heavy bombardment or the precise moment of the Chicxulub impact. Think again.

Tate Britain is hosting a major retrospective of German artist Sigmar Polke’s (1941-2010) work, which is due to end this Sunday (8th February 2015; Herbreich et al., 2014). If you’re in London you should go and see it. Polke’s work spans decades and genres which at first present no surprises; 1960s Pop Art, for the 1970s, magic mushrooms and sex. And then you walk into rooms with a startling explosion of creativity influenced by Polke’s use of materials from the 1980s onwards. Here we find canvases glittering with mica, a large painting depicting a lump of gold ‘Goldklumpen’ (1982) painted with poisonous pigments orpiment and realgar (arsenic sulphides) and green copper arsenite pigments (Schweinfurt Green). Polke also experimented with even more dangerous substances such as uranium based pigments (i.e. Uranium [Pink], 1992); His intention here was to render his art more ‘harmful’.

Polke continuously experimented with materials. He became interested in ancient and traditional painting materials, even producing his own Tyrian purple extracted from seashells (with minor success) to create the painting Purpur (1986). He was also fascinated with modern pigments with interesting optical effects, predominantly composed of synthetic micas coated with thin layers of metal oxides. These included iridescent and metallic car paints and ‘Magic Purple’; the latter having the effect of appearing purple from one angle and then golden from another – this effect could be optimised by burnishing the painted surface, producing rather beautiful paintings including the triptych Negative Value I, II and III (1982).

Polke was fully cogniscent of the fact that many of his paintings would decay and would be beyond the help of the most skilled of painting conservators. He knew that his materials were difficult and would change over time. For example, the orange arsenic sulphide pigment realgar on Goldklumpen has altered to a yellow shade, indistinguishable from the orpiment. However that is not necessarily always going to be the case. One of his ‘pigments’ has remained unchanged for over 4 billion years, however this fact would not help any future forensic analyst of his paintings identify it.

In 1988 Polke produced asigpol006 series of five works entitled ‘The spirits that lend strength are invisible I-V’. Inspired by the ancient land and native peoples of America (Garrels, 2010), these works used a variety of materials and media, including powdered nickel, silver leaf and silver oxides, artificial resins and even Neolithic stone tools (in V, left). Perhaps most striking in terms of materiality is ‘The spirits that lend strength are invisible II’ which is a scatter of powdered meteorite dust dispersed onto artificial resin. This painting, currently on tour with the exhibition Alibis: Sigmar Polke 1963-2010 belongs to The Doris and Donald Fisher Collection.

polke meteorPolke used 1 kg of powdered Tocopilla meteorite to create this painting (right) which is somehow reminiscent of Palaeolithic cave art. Luckily Polke’s use of this material is well documented, otherwise for someone like me, who, perhaps a century from now, will be characterising the pigments used in late 20th Century art, this would come as an unexpected and unrecognisable surprise. It is an extra-terrestrial encounter with unfamiliar materials not found on Earth, except when delivered my meteorites.

The Tocopilla meteorite is one of many associated with the same bolide that was found in 1875 in the Antofagasta region of northern Chile. It exploded in the air before impact and 266 kg have subsequently been collected from a large area of which Tocopilla is just one locality. The find is now known collectively as North Chile (Grady, 2000) and the various and many fragments found have been shown to be chemically identical. Chemically, this is an iron meteorite, probably representing the core of a small planet that was smashed to bits during the early history of the Solar System. More specifically it belongs to a class of meteorites known as hexahedrites and predominantly composed of the iron-nickel alloy kamacite. These are iron-rich meteorites with only approximately 5-6% nickel present. It also contains 3400 parts per billion of the element iridium, which puts in in a class of hexahedrite meteorites known as IIAB (see Morgan et al., 1995).

Just what might a 22nd Century pigment analyst expect to find in this painting? Axon & Nasir (1982) analysed a sample of the 2.5 kg Tocopilla mass owned by the British Museum (now the Natural History Museum). They found that the main mineral kamacite formed large crystals composed of 94.51% iron, 5.05% nickel with a trace of cobalt (0.4%). Enclosed within these crystals were lath- or needle-shaped inclusions of another mineral called schreibersite, an iron-nickel phosphide, (Fe, Ni)3P. Schriebersite is brittle and the needle-shaped crystals form planar features known as ‘rhabdites’ along which the meteorite broke up into its many fragments. Nolze et al. (2006) found tiny inclusions of the chrome-nickel mineral carlsbergite in the schreibersite crystals. Also present are small, massive crystals composed of lamellae of extra-terrestrial sulphide minerals troilite (FeS) and daubréelite (FeCr2S4). None of these minerals would be encountered in terrestrial rocks. Iron does not occur native (even in alloys) naturally on our wet, oxygen-rich planet and although the iron sulphide pyrite (FeS2) is common on Earth, troilite is unknown from terrestrial sources.

SchreibersiteLeft, needles of schreibersite, included in kamacite, radiate out from an iron sulphide-rich grain. This image is adapted from Axon & Nasir (1982). The field of view is about 1 mm across.

Meteoritic material is in the majority ancient. With the exception of rare meteorites know to have been derived from either the Moon or Mars, the vast majority of meteorites solidified in the primordial Solar System. Morgan et al. (1995) used the rhenium-osmium geochronometer to calculate the age of the Tocopilla meteorite and others of similar composition. They found that it is the age of the earliest material known in our Solar System, over four and a half billion years old (4.5 Ga)., over a million years older than the oldest known minerals on Earth. Most meteorites sit in museums or museum archives or are bought and sold by collectors, but at least a part of the Tocopilla meteorite will endure in a most unexpected way on the walls of art galleries. Many casual observers would not know that ‘The spirits that lend strength are invisible II’ is constructed from a material older than our planet. Polke would have known this and therefore his painting’s resonance with deep time, almost beyond imagination. I think this would have satisfied him. Polke created an unique painting with a unique material legacy and one that takes materiality in art to new extremes.

Links & References

You can see some of Polke’s work on the MoMA website here


Image: The spirits that lend strength are invisible II

Image: The spirits that lend strength are invisible V

Axon, H. J. & Nasir, M. J., 1982, A microprobe study of Ni-Co distribution about a schreibersite body in the Tocopilla mass of the North Chile hexahedrite [BM 1931,13]., Mineralogical Magazine, 45, 283-284.

Garrells, G., 2010,

Grady, M. M., 2000, Catalogue of Meteorites: 5th Edition., Cambridge University Press. p. 371.

Halbreich, K., Godfrey, M., Tattersall, L. & Schaefer, M. (Eds.), 2014, Alibis: Sigmar Polke 1963-2010., Tate Publishing, London., 317 pp.

Morgan, J. W., Horan, M. F., Walker, R. J. & Grossman, J. N., 1995, Rhenium-osmium concentration and isotope systematics in group IIAB iron meteorites., Geochimica et Cosmochimica Acta., 59 (11), 2331-2344.

©Ruth Siddall 2015

Posted in Art, Artists' Pigments, Materiality, Meteorites, Minerals, Pigments | Tagged , , , , | Leave a comment

Turacine, Hartlaub’s Turaco and the UCL Grant Museum of Zoology

Further to my recent post on turacine, a pigment extracted only from the feathers of 17 species of turaco, a South African bird, I though I’d check to see if they had any turacos (or their remains) in the treasure trove that is UCL’s Grant Museum of Zoology. They did! Just two feather’s from Hartlaub’s Turaco (Taurcao hartlaubi; catalogue number NON768). There is also a disarticulated skeleton of Buffon’s Turaco (Tauraco Corythaix buffonii; catalogue number 1155). My interest in turacine began when I had read that it was postulated as a potential artists’ pigment by T. W. Salter, in his update of George Field’s “Chromatography”, published in 1869. You can read more about the history of this pigment in my previous post on this blog Turacine: the most unlikely of pigments never to be used by artists

I had very much hoped that the Grant’s feathers may have been donated to the museum by Professor Claude Rimington, once the world’s leading researcher on porphyrins, including turacine, and former professor at what is now UCL’s Medical School. However, the donor is unknown for cat. no. NON768. The feathers were probably given by London Zoo; the reasoning behind this is that some flamingo feathers, with a label in the same handwriting, are clearly labelled as being donated by the Zoological Society of London.

Turacine is a rare pigment and only secreted by turacos in their red plumage. Hartlaub’s Turaco has predominantly blue plumage, with purplish-red pinion feathers on the wings, and luckily it is two of the latter that are in the collection. They were rather old and a bit battered, but nevertheless, they were the real thing which means that I have now actually seen turacin, that rarest of pigments in, as it were, the flesh!

Tauraco_hartlaubi-20081223b IMG_0647

I am very grateful to Jack Ashby, Manager of the Grant Museum, for letting me look at the feathers. I also somehow managed to accidentally adopt a pangolin during my visit.


UCL Grant Museum of Zoology:

Hartlaub’s Turaco; Wikipedia:’s_turaco

©Ruth Siddall 2015

Posted in Artists' Pigments, Colour, Dyes, Grant Museum, Porphyrins, Zoology | Tagged , , , , , | Leave a comment

Turacine: the most unlikely of pigments never to be used by artists

Everyone knows the story of Tyrian Purple, the dye extracted in the Eastern Mediterranean (and elsewhere) and prized by the Romans for its beautiful magenta hue. Everyone also knows that the production of the dye required about 20 billion shellfish to extract enough purple dye to colour a gnat’s handkerchief. I exaggerate, but it was a lot of effort to go to. 2000 years later, chemist and scholar of artists’ pigments, Arthur Herbert Church, a Professor at the Royal Agricultural College in Cirencester during the mid 19th Century, discovered an even rarer animal pigment which, somewhat surprisingly, some thought may have had potential as an artists’ pigment.

MDKern_20120718_1540-Edit-ZF-7303-04679-1-002On 4th May 1869, the treasurer of the Royal Society of London, Dr. W. A. Miller, presented a paper on behalf of Professor Church, entitled “Researches on Turacine, an Animal Pigment containing Copper”. The abstract is printed in the Transactions of that year. Church’s research had discovered a ‘remarkable red pigment’ which he called turacine (later referred to as turacin). This pigment had been extracted from the feathers of several species of a tropical African bird, the turaco. More specifically, it was extracted from “about fifteen of the primary and secondary pinion feathers of the birds in question”. It is now known to be a porphyrin.

Turacos are members of the Musophagidae (“banana-eater”) family, they are also known as plantain-eaters and feast on fruit. They are poor flyers but good climbers, with specially adapted claws for clambering about in trees. Many species do have beautiful, red wing feathers, which were much prized as personal ornaments by Zulu aristocracy. Recent work on turaco phylogeny (Veron, 1999) have identified 23 species, and determined that the 17 turacin-bearing species belong to the genus Tauraco, Ruwenzorornis, Gallirex and Musophaga.

Red-crested-Turaco-Bird-PhotoTuracos do have remarkable pigmentation. Many of the above species are predominantly green and they are the only birds to have a true green pigment which has been named turacoverdin. The colouration in other green-plumed birds is derived from a combination of yellow pigments (such as carotene) combined with optical blue effects. Turacin and turacoverdin are only encountered in turacos. With (1957) states that the red feathers contain up to 5% turacin and are therefore the richest known natural source of any porphyrin. Torben With’s paper in Nature in 1957 identified turacin as an organo-copper complex, with 6% copper complexed with uroporhyrin III.

The biochemist Claude Rimington (1938) relates that Church’s interest in turacine had been piqued when he had been told that the feathers of a bird owned by a Mr Ward of Wigmore Street had released a red pigment when they were placed in a jar of water, and indeed, this process had been much facilitated when soap (an alkali) had been added. Incidentally, stories of turaco feathers losing their colour in water are probably a stretch of the imagination, the birds’ colour does not wash off in the rain! Furthermore the mystery deepened when a pair of turacos, sent to a friend by a military medical officer, based in the Gambia, Dr. B. Hinde, were released into a well-proportioned aviary. Within days the red colouration in their wing feathers had been lost and the feathers were green, much to the disappointment of the new owner. Church deduced that this colour change was due to the loss of copper and subsequently linked this to a diet available only to birds living in their native, sub-Saharan Africa. He postulated that, back home on the veldt, the birds were ingesting grains of copper minerals. In his experiments leading up to his publication in 1869, Church had successfully extracted turacin from four species of turaco.

Church went on to publish a more detailed description of turacine in 1892. A concern over his understanding of this pigment was the essential occurrence of copper and how the birds had acquired this element. In the second paper he rejected the idea that the copper was derived from the birds eating ‘grains of malachite’ or similar copper minerals, and that the copper could be obtained from fruit digested by the birds. Further to the unfortunate discolouration of the birds sent by Dr Hinde, Church had found out that birds living in captivity and fed on bananas retained the red colouration. As further evidence for a fruit-rich diet imparting copper, he cited the work by Italian chemist, Dr Giunti, that amongst other things, hedgehogs contained 0.016% copper and certain lizards contained over 1%. He also went on to say that he had now managed to extract turacine from all species of the bird. The extraction method is given as follows (Church, 1869):

The red parts of the vane are first thoroughly washed with distilled water, and then, after drying treated successively with absolute alcohol and with ether. The material is allowed to dry before being extracted … with exceedingly weak, aqueous ammonia. The crimson solution thus obtained is filtered, and then precipitated by pouring it into a large excess of pure strong hydrochloric acid diluted with twice its bulk of water. … Thus in an operation in which about 4 grms of this pigment were dealt with, it was necessary to increase the volume of the mixture of turacin, hydrochloric acid and water to nearly one gallon before its thick consistency could be so reduced as to permit of its being brought upon the filter. Filters of the finest calico were found to be far preferable to those of paper … the method of vacuum filtration was adopted. All the operations should be conducted quickly; exposure of the moist turacin to light should be avoided as far as possible.”

Church does not say how many feathers were used to extract this dye. However in a latter reassessment of the pigment, Claude Rimington (Rimington, 1938) was able to extract between 0.1 – 0.15 g from the red plumage of a single bird. Research into turacin and its derivatives has continued, thanks to Church’s initial findings. As a unique chemical secreted by turacos, turacin’s value is little more than novelty, though work in the first half of the 20th century found it useful in understanding the biosynthesis of porphyrins in general and hoped it could shed light on the causes and treatment of diseases such as porphyria. Nevertheless, Church’s paper of 1892 is very thorough in its analysis and presents, amongst other things excellent absorbance spectra of turacine, which Rimington could not fault.

Claude Rimington (1902-1993), a professor of Chemical Pathology at University College Hospital Medical School, became the leading authority on porphyrins and continued to work on them for the rest of his life. He published further papers on turacin and collaborated with Torben With (see With, 1957). Rimington had worked in South Africa in the 1930s and these experiences sparked his interest in turaco pigmentation and as a consequence, he became aware of the work of Arthur Church. Rimington, along with his colleagues Ida McAlpine and Richard Hunter published the famous paper of 1968, postulating that George III’s erratic behaviour was due to the condition variegate porphyria, a concept much employed in Alan Bennet’s 1991 play ‘The Madness of George III’ (McAlpine et al., 1968). Anyway, I digress.

Arthur Church was deeply interested in artists’ pigments and published a handbook on the chemistry, provenance and manufacture of pigments and other painting materials, ‘The Chemistry of Paints and Pigments’ a book which in its 1901 edition, became a bible to myself and my colleagues whilst we were compiling The Pigment Compendium (Eastaugh et al., 2004 & 2008). To be fair to Church, he never seriously proposed turacine as a potential artists’ pigment. This speculation comes from his contempory, T. W. Salter, who’s book, another painters’ manual ‘Field’s Chromatography; or treatise on colours and pigments as used by artists’ was published in 1869 when Church’s discovery of turacine was hot off the press. Perhaps Salter had even been at the Royal Society on the day in May that year when Church’s paper was read.

Salter (1869) writes ‘An interesting account has lately been given by Professor Church of a new animal pigment containing copper, found in the feathers of … species of turacus, natives of the Gold Coast, The Cape and Natal. Turacine, the name proposed for it, is noticed here only because it is the first animal or vegetable pigment with copper as an essential element … As the entire plumage of a bird yields not more than three grains of pigment, turacine may be looked upon as a mere curiosity’.

Not unsurprisingly, in a later, ‘modernized’ edition of Field’s Chromatography (Scott-Taylor, 1885), the section on turacine has been omitted. Nevertheless, because of its bizarre derivation we decided to include it in the Pigment Compendium despite the complete lack of evidence supporting its use by any artist (it’s up there with Wongshy Red, another dubious pigment described by Salter). To my knowledge turacin has not been synthesised and indeed Church’s own experiments showed it to be fugitive and susceptible to colour changes (Church 1892). As such it would have been a poor and expensive choice as an artists’ pigment, albeit with an exotic caché. However it does occur to me that Church may well have experimented with it, to see how it painted up. Why wouldn’t he?

Church’s 1869 paper is excellent for its time, though he finishes on an undeservingly self-deprecatory note: “… some excuse may perhaps be allowed for my failure to accomplish more towards the elucidation of a colouring matter so anomalous and costly as turacin.”

Arthur Herbert Church was born in London on 2nd June 1834. He was educated at King’s College London and Lincoln College Oxford, going on to a renowned career as a material scientist with a great interest in the decorative arts. His interests were broad, and he published on porcelain (of which he was a collector), food grains (he worked at the Royal Agricultural College in Cirencester) and minerals, and had been president of the Mineralogical Society. Church had discovered in Cornwall the cerium phosphate mineral churchite. An early exponent of archaeological science, he was honorary curator at the Cirencester Museum of Roman Antiquities. He later lectured at the Royal Academy of Arts. His interest in the chemistry and characterisation of pigments came to fruition in his books, ‘The Chemistry of Paints and Painting’, first published in 1890 and running to four editions. Church was an accomplished amateur landscape painter, and had exhibited in the Royal Academy Summer Exhibition of 1854 and struck friendships with the artists of the day, including Frederic, Lord Leighton to whom he dedicates the painting manual. He also published a book on colour theory in 1907. Importantly, from 1894 Church was responsible for the restoration of the frescoes in the Palace of Westminster, developing analytical and practical methods that were an enormous contribution to art conservation and restoration at that time (Kurzer, 2006). Church was knighted in 1909. He died, aged 81, in Kew on 31st May, 1915.

Whilst we were writing the Pigment Compendium, my colleagues and I often wondered where we would be without A. H. Church and his meticulous research into pigments commonplace and arcane.

So, does anyone have any turaco feathers?


References and further reading

Church, A. H., 1869, Researches on Turacine, an Animal Pigment Containing Copper., Proceedings of the Royal Society of London (1854-1905)., 17, 436–436.

Church, A. H., 1892, Researches on Turacin, an Animal Pigment Containing Copper. II., Philosophical Transactions of the Royal Society of London. A (1887-1895). 183, 511–530.

Church, A. H., 1890, The chemistry of paints and painting., Seeley & Co. Ltd., London, 310 pp.

Eastaugh, N., Walsh, V., Chaplin, T., Siddall, R., 2008, Pigment Compendium: A Dictionary and Optical Microscopy of Historic Pigments. London: Butterworth-Heinemann. 960pp.

Eastaugh, N., Walsh, V., Chaplin, T., Siddall, R., 2004, The Pigment Compendium: A Dictionary of Historical Pigments. Elsevier – Butterworth Heinemen. 499pp.

Kurzer, F., 2006, Arthur Herbert Church FRS and the Palace of Westminster frescoes., Notes & Records of the Royal Society., 60. 139-159.

McAlpine, I., Hunter, R. & Rimington, C., 1968, Porphyria In The Royal Houses Of Stuart, Hanover, and Prussia: A Follow-Up Study Of George III’S illness., British Medical Journal, 1, 5583, 7-18.

Rimington, C., 1939, A Reinvestigation of Turacin, the Copper Porphyrin Pigment of Certain Birds Belonging to the Musophagidae., Proceedings of the Royal Society of London. Series B, Biological sciences., 127, 846, 106-120.

Riley, P., 1993, Obituary: Professor Claude Rimmington, The Independent, Friday, 13th Sugust, 1993:

Salter, T. W., 1869, Field’s Chromatography; or treatise on colours and pigments as used by artists., Winsor & Newton, London.

Scott-Taylor, J., 1885, Field’s Chromatography; or treatise on colours and pigments as used by artists., Winsor & Newton, London., 207 pp.

Veron, G., 1999, Phylogenie des touracos (Aves, Musophagidae). Analyse des caracteres morphologiques., Journal of zoological systematics and evolutionary research., 37(1), 39-48.

With, T. K., 1957, Uroporphyrin from Turacin: a Simplified Method., Nature, 179(4564), 824.

There are some more good pictures of turacos and their plumage on these websites …

A. H. Church: Wikipedia:

©Ruth Siddall 2015

Posted in Artists' Pigments, Colour, Dyes, Pigments, Porphyrins | Tagged , , , , , , , , , | 1 Comment

Building Stones – why should we be interested in Urban Geology?

Urban Geology is the geology of the built environment. This includes the building stones and other materials used in town and cities as well as the tantalising glimpses of the pre-urban landscape and underlying bedrock. Cities are shunned by many geologists and considered as somewhere to escape, and yet many geologists live and work in cities, whether in universities or in the stone, mineral and hydrocarbon extraction industries, and there is much to learn from building stones. Importantly they are an untapped and enormous resource for teaching at all levels. Take the time to stroll down the average shopping street or through the City of London on a sunny Sunday morning and one can find one’s self on a global tour of the Earth’s geology from Precambrian migmatites to Quaternary travertines, from the Jurassic seas of Dorset to the Permian of the Oslo Graben or the Bushveld Complex of South Africa. Here are just a few of London’s examples …

IMG_8898 IMG_8860

Above left, Chandos House on Queen Anne Street is one of the few buildings in London built from Edinburgh’s Craigleith Stone. Above right, a new coffee shop on Mortimer Street has a bar of Madagascan anorthosite.

IMG_7522 IMG_7465

Above left, 1, Poultry is built from a Jurassic sandstone from Helidon, Australia, with stripes of Wilderness Red from the Forest of Dean. On the right, London Metropolitan University’s buildings on Moorgate have columns on Cornish Granite.

The urban landscape is also a great place to learn many aspects of geology, especially from building stones. Whilst there is no substitute for exploring rocks in situ to obtain an understanding of the three-dimensional geometries of outcrops, much can be learned about petrography, petrology, palaeontology and the environment of formation of many rocks on the average high street. The urban geologist is exposed to an enormous variety of rock types, far more than the committed field geologist could ever see in outcrop in the field.

Find out more about the Urban Geology of London from a series of self guided walks. They  are free to download here

The latest walk features Irongate House, an uninspiring 1970s office block that is clad with truly inspiring rocks, a granite-gneiss from near Vredefort in South Africa. This region was hit by a huge meteorite impact 2 billion years ago and the black, glassy melts associated with the impact can be seen cross cutting the polished slabs.

IMG_0033 Left, ‘pseudotachylites’ impact melt glasses form black veins cross-cutting Parys Gneiss from near Vredefort in South Africa on Irongate House on Houndsditch in the City of London.


©Ruth Siddall 2015

Posted in Building, Geology, London, Stone, Urban Geology | Tagged , , , , , | Leave a comment

Jeremiah in Slate Valley: Taconic Slate

Continued from the previous post …

A contributor to the decline of the North Welsh Slate quarries was the discovery and beginnings of industrial scale slate quarrying in the USA. Slate was discovered in Vermont and New York state in 1839, but it did not start to be commercially quarried until the 1850s. Men were needed to work the deposits and this started the first of a series major recruitment drives to bring skilled Welsh slate workers to the quarries of New England. 300 men came in 1891 as the industry boomed and the region became known as Slate Valley.

The slates are Cambrian-Ordovician in age, very similar in origin, and even appearance to the North Welsh Slates. Multi-coloured slates with reduction spots outcrop in the Slate Valley, almost identical to those from the northern Cambrian slate belt of North Wales. Their formation process is similar too. They were formed in a collisional phase of the Caledonian mountain building phase, which here in the northern Appalachians is called the Taconic Orogeny. Mudstones were deposited in a sea which was about to be crushed, uplifted and emplaced westwards onto the continental margin of what was then known as Laurentia. This crustal scale slab of rock is called the the Taconic Allochthon. The deformation initiated in the Middle Ordovician associated with this slice of the Earth’s crust metamorphosed the mudstones into the slates which now crop out in western Vermont and eastern New York State.

My great great uncle Jeremiah E. emigrated to the USA in 1906. He traveled on the SS Umbria, leaving the Port of Liverpool on 10th March 1906, arriving in New York on 18th March. At US immigration he gave his name as Jeremiah E. Williams and his age as 36 (probably pretending to be a little younger than he actually was … or maybe he had just lost count), he was still single and he gave his profession as a ‘miner’. He was able to read and write and his nationality is given as Welsh, his last residence given as Bodegroes, ‘Dolydelen’. This latter fact, unusually recorded in some detail on the record, securely identifies this person as my (half) great great uncle Jeremiah, who had previously lived at Bod-y-Groes farm. He records his intended destination as Colorado and he also states that he was going to see his brother – but oddly the name W. Brown is given here – at the Clear Creek Company in Denver. But Jeremiah did not go to Colorado. Or at least probably not, admittedly, for four years I cannot trace him.

In 1910, we find Jeremiah living in the heart of the Slate Valley in Granville, Washington County, New York, a town very close to the Vermont border. He is 40 (ish), single and a lodger at 290, Quaker Street. His landlord is another Welsh slate worker, Robert Williams, as are the other lodgers in the house. Jeremiah’s precise profession was a slate maker; someone who split blocks of slate into individual roof tiles. Life in Granville was probably not dissimilar to that in North Wales. There were chapels and Welsh was spoken, although Welsh families were not the only immigrants to work in the quarries, quarrymen from eastern Europe, Italy, Ireland and Canada also came, but the Welsh with their skills and experiences were respected, and improved the processes of extraction and often attained positions of authority in the quarries.

On 4th March 1914, Jeremiah was involved in an accident at the Sheldon Slate Quarry where he worked. The following day, the incident was reported in The Troy Times; “Jeremiah Williams, employed at the Sheldon slate quarry, met with serious injuries yesterday, when his leg was hit by a falling stone, fracturing it in two places. Dr McKenzie attended him. Mr. Williams sustained other painful injuries only a few weeks ago.” Who knows what these previous injuries were, but clearly the quarries were not safe places to work. However this incident may not have been pure accident.

On July 15th 1914, The Troy Times reported; “Granville Man Brings Suit. Jeremiah Williams of Granville, a quarryman, through J. C. Jones of Rutland as counsel, has brought suit in Rutland County Court against The F. C. Sheldon Slate Company of Pawlet to recover $3,000 damages on the ground that he received injuries through the defendant’s carelessness while he was at work in the Sheldon quarry March 4, 1914. A scale of slate fell while Williams was in the quarry pit, some of the debris striking him and breaking one leg.” It seems he successfully sued the company for damages, but clearly these riches were not life changing as he presumably recovered and then continued to work in the Granville quarries.

Jeremiah is recorded in the New York State Census taken on June 1st, 1915. He is living at 19, Irving Avenue in Granville (an address also confirmed by the 1915 Granville Directory), again a lodger, this time in the home of David Thomas, another Welsh-born quarryman. Despite his injury, Jeremiah is still recorded as working as a slate maker. However later that year Jeremiah decided to return home. He left New York on the American Line steamship New York which arrived in Liverpool on 19th September 1915. On arrival he gives his occupation as a quarryman and his age as 45, and his destination address as Mount Pleasant, Blaenau-Ffestiniog.

It is at this point I loose track of Jeremiah E. Williams for 30 years. Did he go to work in the quarries of Blaenau-Ffestiniog or did he go somewhere else and live of his claims? Did he have family members in Blaenau? If so, I have not been able to trace them.

In his later years Jeremiah escaped from the quarries and worked on William Williams’s farm in Trefriw. William was married to Jeremiah’s half sister Leah. Jeremiah died in 1942 aged 75. He died at Leah’s home, Crafnant House of a heart attack. He was also suffering from acute bronchial and respiratory problems probably brought on by years of breathing in dust.

CrafnantHouse Crafnant House, Trefriw

So ends what appears to be a life across two continents. Though his sojourn in the USA was brief, less than 10 years, whilst in America, lifestyle, language, religion and work were probably almost exactly the same for Jeremiah as they had been in the quarries of Dolwyddelen, albeit with probably better pay and rights as a worker. However I would like to know more of his experiences, and also why a man, who in comparison to the rest of his family, had a great adventure, was never talked about in the family.


Chan, Y-C., Crespi, J. M. & Hodges, K. V., 2000, Dating cleavage formation in slates and phyllites with the 40Ar/39Ar laser microprobe: an example from the western New England Appalachians, USA., Terra Nova, 12, 264-271.

Goldstein, A., Pickens, J., Klepeis, K. & Linn, F., 1995, Finite strain heterogeneity and volume loss in slates of the Taconic Allochthon, Vermont, U.S.A., Journal of Structural Geology., 17 (9), 1207-1216.

Landing, E., 2012, Time-specific black mudstones and global hyperwarming on the Cambrian–Ordovician slope and shelf of the Laurentia palaeocontinent., Palaeogeography, Palaeoclimatology, Palaeoecology 367–368 , 256–272.

Slate Valley Museum:

©Ruth Siddall 2015

Posted in Geology, New York State, Slate, USA, Vermont | Tagged , , , , , | 1 Comment