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Hohentwiel Phonolite

Material name: Hohentwiel Phonolite
Synonyms: Type 615
Material (geologic): Neogene (Tertiary, Upper Miocene) phonolite

Macrophoto of porphyric phonolite
Foto: Matthias Rummer, 2007

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General characteristics

(In part adapted from Schreiner 1976 and Affolter 2002

Geographical setting: Landscape in the Hegau area
Foto: Rengert Elburg, 2004
  The Hohentwiel is a volcanic mountain in the small region of Hegau in Southern Germany. The natural borders of this area are Lake Constance (Bodensee) in the east, the Rhine in the south, and the Randen Mountains/Swabian Alb in the east and north. The area is characterized by the extinct Neogene (Tertiary) volcanoes, or better volcanic plugs that have been eroded out of their covering by glacial erosion and now stand as crags in the slightly hilly landscape, as illustrated by the photo above.
Material and colour: The material on this page is a intrusive igneous rock of Upper Miocene age (7-8 Myr, Schreiner 1992). The name phonolite comes from the Greek meaning (more or less) "sounding stone" because of the metallic sound it produces if an unfractured plate is hit, hence the English name clinckstone. Normally we wouldn't even think about including a material like this in these pages as its knappability is definitely poor, but it seems that it was used in prehistory for the manufacture of knapped stone tools (see sections below).
It is a predominantly grayish brown to greenish gray, sometimes very dark gray rock of porphyric structure (i.e. it has a very fine-grained matrix with larger crystals embedded in it), consisting mostly of feldspars and feldspathoids like nosean, sanidin and egerine with some hauyn and nepheline (Schreiner 1992: 101). In how far this source can be differentiated from other similar materials, e.g. the other phonolite volcanoes in the Hegau, is unclear.

The original description as a prehistoric raw material by Affolter (2002: 259) is, roughly translated:
"The type 615 is not a silex but has been knapped with the same techniques during the Magdalenian, as it is similar to a siliceous rock. It has a glassy appearance, the colour is dark green, mottled with lighter spots. In fact it is an intrusive rock that is exposed at Hohentviel (sic) near Singen. This massive material gives quite rough surfaces, but is easily knapped. Used locally during the Magdalenian, it has been circulated up to the centre of the Swiss plateau."

Other information: Until now, we saw the phonolite from Hohentwiel only mentioned once in the archaeological literature as a stone age raw material. Exploitation will probably have been limited to picking up fine-grained scraps and pieces from the surface beneath the steep cliffs.
Knapping notes: If we hadn't the word from a well-known and very knowledgeable lithic specialist on the fact that the stuff indeed was used for the production of flaked stone tools, our verdict would be: unknappable. As you can see in the photos towards the bottom of the page the fracture is mostly quite flat and irregular, instead of nice smooth and conchoidal. And these are the pieces we found that would constitute the best raw material; most other stones contain larger phenocrysts, have an even more crystalline matrix, or just split in flattish pieces instead of fracturing with a sharp edge. If it were the only solid stone for miles around, I could understand that you would use it in case of emergency, but the fact is that there are quite a few sources of decent chert in the region (Fritsch & Neubauer 1987).
Archaeological description: According to Affolter (2002: 177) the phonolite of Hohentwiel was used as a raw material during the Upper Palaeolithic (Magdalenian). It has been identified on two archaeological sites in Switzerland: in the abri of Kesslerloch near Thayngen (less than ten kilometres to the west-southwest near Schaffhausen) and at Neuchâtel-Monruz (at the shore of Lake Neuchâtel, over 160 kilometres to the southwest). In the case of the Kesslerloch it is clearly a local (substitute) material, but the presence in the west of Switzerland could be one of the classical cases of more or less direct proof of prehistoric mobility that can only be discovered by the sourcing of raw materials.
It would be interesting to see if the phonolite is present in the other famous Magdalenian site in the region, Petersfels (some eleven kilometres north of Hohentwiel), too. We haven't seen it mentioned in any publication yet, but we'll make sure to view the literature on the lithics of Petersfels in the near future.

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Locality: Hohentwiel near Singen, Hegau, Baden-Württemberg, Germany
Synonyms: Singen/Hohentviel (Affolter 2002)
Geographical description: The Hohentwiel is a large stump of intrusive rock that has been eroded out of the surrounding molasse and tuffs directly to the west of Singen in southern Germany, just north of the border with Switzerland. On top of this rock, which rises 260 metres above the surrounding country, lie the ruins of a fortress.
Geographical co-ordinates: Lat. 47° 45' 49.6" N
Long. 008° 49' 02.8" E
(Mapdatum WGS 84)
Co-ordinate precision: The coordinates point to the southern side of the top, near the entrance to the castle, where the picture below was taken. As there are quite a few very steep cliffs surrounding the fortress, it would be a very bad idea to try and reach this point as the crow flies or during times with limited visibility like at night or in dense fog. Better follow the path which leads up.
Other topographical information: The city of Singen is easily reached by motorway, although it lies in a corner somewhat cut-off from the rest of Germany, and has good train-connections too. When you are in the town, you really can't miss the Hohentwiel, which dominates the complete view towards the west. You can drive about half-way up the mountain, but the last few hundred metres have to be done on foot. It is a very nice walk, although you have to gain quite a bit of height.
Additional information: Sampling site with castle
Foto: Rengert Elburg, 2004
  In the picture above you are looking toward the topmost ruins on the Hohentwiel. The whole summit is surrounded by fortifications, for which an entrance fee is due. The spot where the photo was taken is just outside the inner area and can be visited for free, around the clock.
Visitors information: Museum in Unteruhldingen
Foto: Rengert Elburg, 2004
  Singen itself is, I am sorry to say, not a nice town. Although the settlement dates back well into medieval times, it only became a city at the end of the 19th century after is had expanded due to the establishment of the large Maggi factory. So the city owes its present size and form to instant-soup and the horrible condiment from the same source. But it has a small archaeological museum, the Hegau-museum, and there are plenty archaeological and other sites and sights in the area.

For the palaeolithically inclined there are the Kesslerloch near Thayngen, just over the border in Switzerland, and the Petersfelshöhle near Bittelbrunn, well known for its Magdalenian figurines. For those interested in more recent prehistory, a visit to the reconstructed Neolithic and Bronze Age lake-side dwellings in the Pfahlbaumuseum near Unteruhldingen on Lake Constance is a must (photo above). Very worthwhile, when you are in the region, are the Romanesque churches on the island of Reichenau, a UNESCO World Heritage site. And if you have come this far, do visit the city of Konstanz and the archaeological Landesmuseum.

Further sights in the region are the Donauversickerung or Danube Sink near Immendingen where a large proportion of the (here still quite narrow) Danube is drained by karstic fissures. Nearly half the year, the complete river disappears into the underground, feeding a very large karst spring at Aach, eleven kilometres to the southeast, which is worth a visit too.

As for places to stay: drive down to Lake Constance, here camping grounds and hotels abound.

Sampling information: As the whole mountain is made up of phonolite, you don't have to look for an exposure: the stuff is everywhere. Just pick up loose fragments and test them. Better not hack around too much within the fortress at the top, as this is probably not going to make you very popular with the personnel.

There are several other sources of chert known in the region (Fritsch & Neubauer 1987, Affolter 2002) which you might want to visit too. We hope to bring more information on these materials in the future.

  Fresh flake
Foto: Matthias Rummer, 2007
Flake of reasonably fine-grained material
size: 54 mm
Greenish piece
Foto: Matthias Rummer, 2007
Example of the more greenish material
length: 50 mm
Sample description: The piece to the left above gives a good idea of what the material looks like in a fresh state. The colour of the matrix lies around 5GY 5/1 to 4/1 (greenish gray to dark greenish gray) to 5GY-10Y 4/1 (dark greenish gray), according to the Munsell scale. You can see some phenocrysts as well as less clearly defined patches of lighter material. The photo next to it is slightly overexposed, but shows clearly that there is a strong greenish component in the dark colouring. The fracture is quite irregular and hampered by the larger crystals.

The piece on the left below is just another example of the phonolite. At the right we included a natural piece with a relatively smooth fracture-surface which shows slight patination bringing the colour to 5Y 5-6/2, a (light) olive gray.
The last photo is a close-up of a very small flake where you can see the rough texture of the fracture and some very light phenocrysts.

  Coarse material
Foto: Matthias Rummer, 2007
Piece with irregular fracture pattern
length: 72 mm
Patinated piece
Foto: Matthias Rummer, 2007
Natural, slightly weathered piece
length: 49 mm
  Porphyric structure
Foto: Matthias Rummer, 2007
Very small flake with phenocrysts
width: 19 mm


Last modified on:
January 16, 2008
Contents primarily by:
Rengert Elburg
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