European Geologist Journal 48

Featuring slate:
the German geoheritage initiative “Rock of the Year” in 2019

 

by Christof Ellger1 and Manuel Lapp2

GeoUnion Alfred-Wegener-Stiftung, c/o Institute of Geosciences, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam

Saxon State Agency for Environment, Agriculture and Geology, Halsbrücker Straße 31a, 09599 Freiberg

Contact: Christof.Ellger@geo-union.de


Abstract

Since 2007 the geoheritage initiative “Rock of the Year”, spearheaded by the Berufsverband Deutscher Geowissenschaftler, BDG [German Professional Association of Geoscientists], has strived to communicate essential aspects of geology to the general public in Germany. Each year, a specific type of rock is chosen to be featured in publications, media news and events, with the aim to inform the audience about the importance of geosciences, about geology and petrography in Germany, and about the rock industry. In 2019, the choice of slate as a particularly attractive ‘rock of the year’ prompted a series of media products and events, successfully featuring the rock and its origins, its qualities and its use, both in history and today.


In its 13th Year: the “Rock of the Year” Initiative in Germany

The initiative “Rock of the Year” was started in 2007. Following the model of other “… of the year” activities in Germany, a group of geoscientists with a strong interest in geo-communication and outreach, led by Werner Pälchen and other members of the Berufsverband Deutscher Geowissenschaftler BDG [German Professional Association of Geoscientists] proclaimed “rock of the year” as an instrument to communicate aspects of geology, geoheritage and the stone industry into the wider public.

Year-based communication initiatives in Germany had begun in 1971, when one of the larger conservationists’ associations in Germany (NABU – Naturschutzbund Deutschland [Association for Nature Conservation Germany], then under the name of Deutscher Bund für Vogelschutz [German Association for the Protection of Birds]) made the peregrine falcon (Falco peregrinus) “bird of the year”, unleashing a tremendous series of annual campaigns for nature objects. A current compilation (https://de.wikipedia.org/wiki/Natur_des_Jahres) lists 47 nature elements of the year for Germany, from mushroom of the year to seabird, single-celled organism, potato or mollusc of the year. And it is not just about flora, fauna and, for that matter, mycobiota; there are also larger nature components highlighted year by year: the landscape of the year, the river landscape of the year, the tree-lined allée of the year, and—also in the geosciences and important in the geoscientific community—the soil of the year (Deutsche Bodenkundliche Gesellschaft [German Soil Science Society] and Bundesverband Boden [Federal Soil Association], since 2005) and the fossil of the year (Paläontologische Gesellschaft [Palaeontological Society], since 2008). The idea has also spread beyond nature and wildlife; e.g., there is a public monument of the year (since 2004) or a musical instrument of the year (since 2008). Interestingly, although rather self-evident and convincing in its potential, this idea of the ‘year elements’ does not seem to have been taken up to much extent outside the German-speaking countries.

For 13 years now, BDG has led the “rock of the year” initiative. It set up a small committee with experts from BDG, from geological survey institutions in Germany, from the stone industry and from geotourism, which decides on the respective annual rock and on the measures to communicate this to the society.

The background for this activity of rock of the year—and also the major reason why it is so important—is the fact that the general knowledge about geological issues in Germany is actually very limited. Apart from a small number of exceptions, geology is virtually not taught in schools, which leaves the existence of geoscientific knowledge to the small group of experts with geological university education and the community of interested amateurs. In this situation the “rock of the year” initiative is one step in the endeavour to get more information about geosciences into people’s heads in Germany. In the almost 13 years of its existence, this has been more or less successful. In the media, the rock of the year is well-established by now as one of the elements of nature which are being presented during one year. A series of flyers and booklets have been produced for the rock years, “rock of the year” is published on the internet, by BDG and  GeoUnion Alfred-Wegener-Stiftung (the federation of the geosciences associations and research institutes in Germany) and the Geological Surveys of those federal states which have the annual rock in their geology. A number of major events are staged. Every year, the festivities start in spring with the “baptism” of the rock, usually at a major deposit and mining location of the rock of the year, organised by BDG, the stone industry and the company owning the “baptism” quarry. The rock of the year is ceremoniously baptised, with either wine, champagne or beer, depending on the favourite drink—or even local product—of the region. Other events follow: Geological Surveys of the federal states present the most attractive outcrops of the rock of the year, also proclaiming a “rock of the year geosite”, in their territories with public manifestations. Annually in September the Germany-wide held “geosite day” [Tag des Geotops]—another initiative of geoscience outreach in Germany (since 2002, every year on the third Sunday in September)—is used for public presentations of the rock of the year in various parts of the country. In addition, natural history museums may take up the idea and present the annual rock in a special showcase. Finally, the rock of the year is also featured in Germany’s geoparks, provided of course that there is an outcrop; by autumn 2019 the number of ‘national geoparks’ reached 16, of which six are also acknowledged as UNESCO Global Geoparks (http://www.nationaler-geopark.de/startseite.html).

One fundamental aspect of petrology is already part of the selection procedure for the rock of the year: the classification of rocks into three major groups—igneous, sedimentary, metamorphic—is of course taken into account in the choice of the rock of the year, as the committee tries to cover the three categories equally, ideally taking turns every three years. This has essentially been adhered to as the list of the past “rocks of the year” shows (https://de.wikipedia.org/wiki/Gestein_des_Jahres):

2007    Granite                        igneous
2008    Sandstone                  sedimentary
2009    Basalt                          metamorphic
2010    Limestone                   sedimentary
2011    (Volcanic) Tuff            igneous
2012    Quartzite                     metamorphic
2013    Kaolin                           sedimentary
2014    Phonolite                     igneous
2015    Gneiss                          metamorphic
2016    Sand                             sedimentary
2017    Diabase                       igneous
2018    Black coal                    sedimentary
2019    (Roofing) Slate            metamorphic

Naturally, there are other criteria and intentions involved. For instance, in order to feature the variegated aspects of sand as a resource, the committee made ‘sand’ rock of the year in 2016, although sand, of course, in the scientific sense of the work, is not a (solid) rock but rather granular rock material of a specific grain size. On the other hand, sand consists of rock material and therefore the choice was accepted as cum grano salis (to mention grain just once again).

There are several motives associated with the annual rock campaigns and their contents: firstly, general geological knowledge and a basic understanding of the key concepts of geology (and petrography, for that matter) are to be communicated into the public: the classifications of rocks, their essential features and also their origins, and in combination with the latter their distribution (in Germany, in Europe and also worldwide). The rock of the year is also used to enter into the presentation of fundamental elements of Earth History, geological eras and formations, and essential processes in geology like volcanism, weathering, sedimentation and metamorphosis. And there are questions of geomorphology and geoecology: Which landscapes are associated with given rock types? How do rocks influence the ecosystem, including the quality of the soils? Secondly, for BDG and the rock of the year committee there is a strong interest in the use and the economic importance of rocks: What can we do with specific types of rocks? How have they been used in history? How has the use of certain rocks characterised the cultural landscape in European regions, with regard to both the quarrying activities and the built-up areas? And which products of our daily routine (like glass, paint or toothpaste) depend on which rocks (like sand, gypsum and limestone)? And, after all, features in our every-day world have a greater chance to be esteemed and preserved for the future if we are aware of their value. People will support and strive for the conservation of slate as both an architectural element and landscape feature only when they know what roofing slate is, looks like and means in terms of geology, earth history, regional history, tradition and aesthetics and how it differs from, say, asbestos cement elements on roofs and walls.

Rock of the Year 2019: Roofing Slate

Slate: the very special metamorphic rock

For 2019, slate was chosen as “rock of the year”; what is essentially meant here is roofing slate (Figure 1). In German, there are some terminology problems due to the fact that the German word for slate, “Schiefer”, has a wider connotation than its English counterpart and is also used for certain (high-metamorphic) schists on the one hand and certain shales on the other hand, i.e. sedimentary mudrocks with slate-like properties. Therefore, one of the first tasks of ‘teaching’ slate to the public is to clarify these terminology issues and distinguish between the different types of “Schiefer”. All these slates and slate-like rocks show foliation, the “slaty cleavage” which means that the rock disintegrates in flat sheets. Really fine plane sheets, however, can only be cut from the “real” low-metamorphic slate as a result of its fissility, which the rock owes to the lateral pressure effect on its mineralogical fabric during metamorphism (Wichert, 2017).


Figure 1: Roofing slate at the historic slate mine at Lehesten, Thuringia (Photo: Susen Reuter).


More than many other rock types, the attractive slate is certainly an excellent choice for a public outreach initiative, especially in Germany (this would, of course, be similar in e.g. Wales, France, northwestern Spain and northern Portugal). As a rock type and building material slate is very specific, and in a number of areas in Germany slate is common and well known.

Slate in Germany: spatial distribution and (historical) uses

There are several areas in the country where slate used to be mined extensively for centuries, and there are large regions where slate has been used as the dominant building material. Two of the major Central German Uplands mountain ranges were named after slate: Rheinisches Schiefergebirge (“Rhenish Slate Mountains”, internationally known as the Rhenish Massif), the large Western tract of the Central German Uplands, and Thüringer Schiefergebirge (“Thuringian Slate Mountains”, Thuringian Highland) as a somewhat smaller part of the Uplands in Thuringia, actually also covering parts of Franconia and Vogtland (Schubert & Schubert, 2015) (Figure 2).


Figure 2: Roofing slate areas and major production regions in Germany (Map design: Angela Ehling, BGR).


Figure 3: Slate used on roofs and facades; house in Ludwigsstadt, Upper Franconia (Photo: Christof Ellger).


Figure 4: Roof material provinces in Germany (Map design: H.W. Wagner). Source: Wagner 2018, p. 10.


The Central German uplands are essentially the result of the Variscan (Hercynian) orogeny. And it is here that we find the slate, because it originated from pre-Devonian marine-coastal clay sediments, compacted after sedimentation and subjected to diagenesis and metamorphism in this Variscan (Hercynian) orogeny. It is these remaining areas of the Variscan belt which bear the slate, next to Paleozoic limestones, sandstones (greywacke), but also plutonites, metamorphic and volcanic rocks in the complex uplands geology.

Major historic slate mining areas in the Rhenish Massif are Eifel (south of Cologne and west of Koblenz (Friis, 2018) and, slightly further south, Hunsrück; Sauerland (south of the Ruhr area) in the northeastern part of the Rhenish Massif. Further east, slate mining was important on the northern edge of the Harz Mountains, in the border area between Thuringia and Franconia and on the edge of the Erzgebirge (Ore Mountains) in Saxony.

The major product from slate was—and still is—roofing tiles and, to a lesser extent, façade cladding tiles. In the slate mining regions roofs and also walls were covered with slate, which made these regions specific slate construction provinces (Wagner, 2018) (Figure 3). Given the regionally available resource for making tiles, roof material provinces can be distinguished in Central Europe (Figure 4). But slate was also exported, transported by ships on rivers and later by railway to major trading centres, territorial capitals or important ecclesiastic centres. From the Middle Ages until the 19th century, roofing slate was appreciated as the optimum material, fine and durable, for roof covering for prestigious buildings all over Germany. A large proportion of the buildings with UNESCO world cultural heritage status, like Aachen Cathedral (Figure 5), have a slate roof (Stahr, 2018).


Figure 5: Aachen Cathedral (Photo: CEphoto, Uwe Aranas, Wikimedia Commons).


Most of the slate mining in Germany has ended as production was no longer competitive with other European and global slate producers and—more crucially—with other construction materials. Five slate mines have survived. Most roofing and cladding slate is now imported, predominantly from Spain, Portugal, Brazil and China. This means that slate is still available for the refurbishment of old existing slate roofs, even if not necessarily slate from German mines. Helped with interesting product innovations by the slate producers, there is something like a renaissance in slate construction currently, slate being used not only for roofs and the cladding of exterior walls but also for the interior, for floors, walls, stairs and baths.

The other historically relevant slate product was writing slates and blackboards. A century ago, classrooms all over the world were equipped with writing slates and blackboards, often enough from Germany, essentially from the Thuringia-Franconia slate area, where several museums highlight the history of the production of writing slates. An excellent exhibition can be found in the slate museum in Ludwigsstadt, Upper Franconia; slate in schools is focused on nearby in Steinach’s local museum.

Celebrating slate in 2019: major events and activities

The year of slate was announced in January with press releases which were issued through various channels. A number of newspapers and internet publishers used text and photos for an article. The main opening event for the year of slate was the inauguration of the rock of the year on 3rd May, with the ceremonial christening of the slate: the event was held in the city of Mayen (Rhineland-Palatinate; on the edge of the Eifel Mountains) at the company headquarter of Rathscheck – Germany’s largest slate producer – which itself is a fine architectural masterpiece capable of advertising the use of slate in construction. Before the moment of christening, the slate presentation involved a number of topical speeches by representatives of BDG, the Geological Survey of Rhineland-Palatinate, the mineral resources industry and also by the representatives of Rathscheck, the host company, who gave an overview on slate in geology, mining economics and architecture. In Mayen, the slate was, aptly, baptised with slate Riesling, white wine from the nearby Mosel area, where the wine actually grows on slate soils (Figure 6).


Figure 6: Christening slate as rock of the year 2019, May 3 2019, Mayen (Photo: Rathscheck Schiefer).


An extended fanfold leaflet covering all the essential aspects of the rock’s geology, mineralogy, deposits as well as the (historic and present-day) use of slate was produced by the Geoscientists’ Initiative in Berlin and Brandenburg (Geowissenschaftler in Berlin und Brandenburg), directed by the rock expert Angela Ehling, assisted by Wolfgang Wagner, another slate specialist in Germany. Also as part of the “rock of the year” (and similarly to preceding years), a number of Geological Surveys of the federal states published separate leaflets and internet pages on “their” slate, presenting both slate in general and the slate locations with their products in their territories. A poster for the Rock of the Year 2019 was designed by BDG, again in cooperation with Rathscheck.

In addition, several individual lectures on slate were organised in various cities in Germany. Given the potential to use the topic of slate to convey a larger range of general aspects of geology and the geosciences as a whole into the general public, GeoUnion Alfred-Wegener-Stiftung organised a lecture series for town libraries, adult education centres and similar institutions which was marketed all over the country. As a result, about 25 lectures will take place in towns of very different size throughout Germany during this slate year. Using slate as the key to open up the discussion, the basics of petrographical classification, questions of geological age and stratigraphy, tectonics and the changing configurations of continents and oceans are featured in the lectures. Other topics covered include slate mining then and now and the economy of the slate industry, and there are themes ‘beyond geology’, like wine-growing on slate (along the rivers Rhine and Mosel) and the use of slate in works of art. With respect to the latter aspect, there are a number of artists in Germany who work with slate. A fine present-day example of a slate art project is “Grauzone” (grey zone): the artist Bernard Misgajski, who lives and works on the Isle of Rügen, found and rescued disused slate tiles (originally from Wales!) from the roof of a railway shed in the Danish harbour of Gedser and distributed them to colleagues of his. As a result, 37 artists from five countries produced twin works, with the Gedser slate tiles on the one hand and an artistic reflection (using any other material) on the other hand, for an exceptional project exhibition (DIE BEGINEN e.V. 2019) (Figure 7).


Figure 7: Josef A. Kutschera: Landzunge (Promontory), 2018, from the art project ‘GREYZONE – a roof becomes art’ (Photo: Christof  Ellger).


Conclusion

Thirteen years after its start in 2007 the German geology and geoheritage initiative “rock of the year” has become well-established in the geoscience community and well covered by various media. 2019, the year of slate, appears as a special highlight, with a fascinating multifaceted stone. The challenge for the future will be to select rocks that are sufficiently attractive for the media and the public. This encompasses both the attractiveness for the general audience to get them closer to geological issues and the potential for associations and companies to communicate their interests. The initiative itself may improve itself substantially by a range of measures, e.g. with a specific website for the rock of the year and with improved networking between the rocks associations and all the other institutions involved.


References

DIE BEGINEN e.V. 2019. GRAUZONE. Ein Dach wird Kunst. (GREYZONE. A Roof Becomes Art). Rostock: Der Rostocker Frauenkulturverein DIE BEGINEN e.V.

Friis, C. 2018. Der Moselschiefer in der Osteifel: seine Entstehung, sein Abbau und seine Fossilien (Mosel slate in the Eastern Eifel: its origin, its mining and its fossils). Kottenheim: Selbstverlag Claus Friis

Schubert, R., Schubert, J. 2015. Unser “afrikanischer” Schiefer: Die Geologie der unterkarbonischen Dachschiefer- Lagerstätten im Thüringisch-Fränkisch-Vogtländischen Schiefergebirge (Our “African” slate: The geology of the Lower Carboniferous roofing slate deposits in the Slate Mountains of Thuringia, Franconia and Vogtland). Leutenberg: Naturpark Thüringer Schiefergebirge/Obere Saale

Stahr, M. 2018. Schiefer. Ein natürlicher Baustoff an Dach und Fassade (Slate: A natural construction material for roof and wall). Bausubstanz: Zeitschrift für nachhaltiges Bauen, Bauwerkserhaltung und Denkmalpflege, 9/3. 45-53.

Wagner, H.W. 2018. Dach- und Wandschiefer – ein traditioneller Baustoff in Mitteleuopa: mit einer Karte der traditionellen Schiefer-Dachlandschaften als Beitrag zur Orts- und Dachgestaltung (Roofing and walling slate – a traditional construction material in Central Europa; with a map of traditional slate roof landscapes as a contribution to village and roof design). Veröffentlichungen des Netzwerkes „Steine in der Stadt“, 1/2018. Hanover: Netzwerk “STEINE IN DER STADT”

Wichert, J. 2017. Roofing slate – origin, deposits, properties, standards and mining. Ph.D. thesis, Technische Universität Bergakademie Freiberg


This article has been published in European Geologist Journal 48 – Geological heritage in Europe. Read here the full issue:

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