The kieselguhr was covered by gravel and sand from the last ice age with a thickness of 4 to 10 m. This enabled open pit mining.
The kieselguhr deposits are divided into three deposit layers: The "white gur" is the top layer. In some places it is also stored directly below the surface of the earth. At three to five percent, it contains very few organic components. In the early years, only the white gur was mined. The organic components of the “grey gur” were later removed by burning. As a result, the bottom layer, the "green gur" could also be mined. The "Green Gur" contained the highest proportion of organic components and was located in the area of the groundwater table.
The pitfalls of kieselguhr mining: A major environmental problem in the mining of kieselguhr was the groundwater that accumulated in the pits. The introduction of the extremely acidic mine water into the Sothriethbach, which was once rich in fish, turned this into a dead body of water over long stretches. The pungent odor of the sulfuric acid vapors escaping from the stills also annoyed the population of the surrounding villages.
Domestic kieselguhr mining was discontinued when mining became unprofitable because the gur could be imported more cheaply. Mining in northern Germany finally ended in 1994.