The Oderteich is a lake in Lower Saxony, Germany. The lake served as water reservoir for downstream mining activities (Sankt Andreasberg), nowadays being used also for recreational purposes. We had a stop at the lake during our trip to Harz and could observe the lake surroundings from close distance. The water has a reddish color given by dissolved humid acids from dead plant materials.

Oderteich Oderteich

We noticed some big blocks of granite around the lake and were interested to know more about them. It seems that the lake has been completely surrounded by granite but with time, this has been eroded by transformed in sands and gravel. However, some boulders are still present as a prove of geological transformation in the area and look like swimming in the sandy material towards the water. Walking around the lake I was able to get a small sample for my Sand Atlas (sample no. 2296):

2296 DE-NI Germany - Lower Saxony - Oderteich
Germany – Lower Saxony – Oderteich

Questenberg is a small village with 350 inhabitants in the southern Harz and we just learned about it from the Geopark Harz leaflet no. 12. The village was mentioned in the guide for the presence of alabaster balls outcropping at the surrounding slopes. Alabaster intrusions are small, ball-like gypsum deposits concentrated within the mother rock. We have spotted the area from the main road but the slope was so steep, so we couldn’t have a closer look. However, we found a hiking trail leading to the hill top so we decided to give it a try. Climbing up the forest path we passed by some crumbly boulders.

Weathered gips block Gypsum at Questenberg

The nearby info tabs explained us that we find ourselves on a huge anhydrite deposit. Anhydrite (CaSO4) is a white (sometimes grayish) mineral that, in contact with water, it transforms to the more common gypsum (CaSO4·2H2O). So the boulders we have seen were most probably made of old gypsum rock, assumption confirmed after arriving on the top of the hill. The soft gypsum rock was eroded by rain and wind action to a fine powder and I couldn’t pass by without taking a small sample for the Sand Atlas collection.

The image above shows the surface of a small conglomerate. The material was rather unconsolidated and turned into a beautiful white sand just by pressing with fingers. The dark tone is from lightning, the material is almost white in reality.

But, although surrounded by gypsum (photo left), Questenberg is known for another reason: the legend says that the castle lord lost his daughter in the nearby forest. The desperate father asked for help at the inhabitants of the surrounding villages and found the girl on the third day of Pentecost holiday with a crest with two tassels. The castle lord was extremely happy and payed a lot of favors to his people. Since that day, every year the inhabitants of Questenberg raise a wooden symbol on the gypsum mountain in respect to their former castle lord (figure right).

As I wrote in a previous post, Harz region has been born from a sea bottom several hundreds of millions years ago. The remains of seashells and other marine animals have piled up and turned into a thick limestone layer which found its way out to the surface. An old quarry can be seen left exposed at the side of the road near Wernigerode, a beautiful city in the north of Harz. In the immediate vicinity of the quarry one can see an old defense tower dated back to the 11th century. At a closer look at the walls of this tower we could see small round seashells as a prove of the former marine origins of its construction bricks:

Small rounded seashell fossils from 285 million years ago in an old limestone quarry

Perhaps one of the most impressive moments during our trip to Harz mountains was visiting the Iberg Dripstone Cave (Iberger Tropfsteinhöhle). The cave is located on the western side of the mountains near Bad Grund city and is formed within a chalk deposit, a former coral reef about 385 million years ago. The cave was discovered in 16th century by miners but only opened to the public access in 1874.

In 2008, the cave administration opened the so-called Cave Experience Center with three components:

  • Museum in the mountain (Museum im Berg) – a long gallery before the cave entry with nicely designed panels showing the formation of Iberg Dripstone cave from a coral reef and the movement into actual location.
  • Fascination cave – the cave itself (partially opened to the public) with amazing dripstone formations
  • Museum on the mountain (Museum am Berg) – the most impressive part of the complex: an extraordinary journey through the life and existence of ancient people living in a nearby cave.

The 30 minutes spent inside the cave were more than worthy but the museum installed outside topped them all: absolutely lovely way of combining graphic elements with informational content for waking up the visitors interest:

Iberger Cave Adventure Center
Inside the museum at Iberg Cave Experience Center

The museum focuses on a very exciting theme: human skeletons of 40 people have been found in another cave (Lichtenstein cave) located not far away from the complex. The group was a family clan living about 3,000 years ago in the Bronze Age, the cave having most probably a graveyard function. The most exciting part is the DNA information collected from the bones: it perfectly matched the DNA structure of 15 local people living nowadays nearby the cave. This amazing discovery has been reported as the “oldest family tree on earth” with direct genetic links over a time span of 3,000 years. Moreover, using modern techniques, the scientists could re-create the upper body parts of three members of the family clan. The exhibition at Iberg Cave Experience Center shows detailed information about their daily life, food gathering and preparation, plant and animal rests, tools, etc. And everything displayed in an absolutely professional manner – we highly recommend a visit to anyone travelling to Harz region.

Some people may complain that German natural landscape is rather unspectacular. The North Sea and Baltic Sea in the north, some mountains in the south and not so much in between. Well, for those who may think like that I strongly recommend a visit to the… Harz region!

Why is Harz so interesting and why am I writing about it on the Sand Atlas website? The answer is because Harz is maybe one of the most geologically diverse region in Germany with dramatic changes within very small areas (from here the nickname “Classic Geological Square Mile”). Nowadays Harz is a low mountain range stretched over 180 km long and 30 km wide with the highest peak, Brocken, at 1,141 m. Things get more exciting when we look back over several hundreds of millions years ago, when all continents were “glued” together forming one single piece of land called… Pangaea. At this time, Harz was located much closer to Equator than now, somewhere on the actual location of… Cairo. When Pangaea began to split in two super-continents (Gondwana and Laurasia), the water started to fill the gap between them. Also the Harz was covered by water and abundant sediments transported from the vicinity started to pile up on the sea bottom.

Reproduction of the Earth from Late Triassic (about 220 million years ago) showing the separation of Gondwana (in the south) from Laurasia (north) – source: Wikipedia Commons

Further on, various tectonic events caused the creation of faults and uplift movements, exposing the various rock deposits to the surface. Due to their high altitude the new formed mountains were quickly eroded (especially the upper new layers) and the underlying base rock was standing as low mountains. These processes led to the formation of numerous types of sedimentary, igneous and metamorphic rock deposits. Among the upper layers, most common are the argilaceous shales (German: Schiefer), greywackes and granite. and from the older ones, limestone and gypsum deposits.

Maybe so far nothing really extraordinary but, as I said before, the true beauty of Harz geological architecture is given by the density and diversity of geological formations. On small areas, massive metal ore deposits are for example accompanied by lignite and salt deposits, limestone beds or dolomite formations. This high availability of minerals and valuable elements gave the region important mining privileges for metal ores (Fe, Mn, Pb, Zn, Ar, Au etc) while the soft calcareous deposits provided the formation of many drip-stone caves and caverns.

During a four-day drive-and-camp trip in Harz we collected several samples and learned a lot about specific geological features. More details about the trip with large descriptions of individual locations are in preparation and will be posted within the next days.

The internet is also full of information about Harz but our preferred website is The website is very informative and there you can download 18 leaflets in both German and English language (partly also in French) about the geological landmarks of the region.