Raw materials in the Geopark Porphyry Land: Treasures from the Earth’s history
The hidden treasures of the Geopark Porphyry Land
Buried beneath the Earth’s surface lie treasures that have been and continue to be fundamentally important for the development of human life, culture, and economy. These raw materials are extracted from the Earth and either used directly, such as stones, or require further processing. Unlike water, the availability of most of these resources is limited, because they cannot be renewed. They were formed by specific geological processes, which typically lasted for millions of years. In our geopark, these treasures consist mainly of volcanic rocks formed by caldera volcanism on the supercontinent Pangaea around 290 million years ago. During the Tertiary period and the more recent ice ages, these rocks were either eroded or transformed, and now only exist as remnants.
Specific mineral resources in the Porphyry Country Geopark
Groundwater and thermal water
Water is a special (raw) material. Of the approximately 1.4 billion cubic kilometres of water on Earth, just under three percent is fresh water, which is vital for human life. On average, about 70 cubic metres of water per second flow down the Mulde towards the Elbe. The waterworks between Naunhof, Grimma and Thallwitz extract water from the glacial gravel and sand layers of the Mulde and Parthe rivers to supply drinking water – up to 2,000 cubic metres per hour in the Canitz waterworks alone.
The thermal water of Bad Lausick, which is very rich in iron due to former lignite mining, has been used for therapeutic purposes since 1821.
Sand and gravel
These are deposits that formed the floodplains of the Mulde and its tributaries 400,000 years ago when the ice sheets of the Elster and Saale glaciations melted. Sands and gravels are widely used as construction materials: as plaster and mortar sand, filter material, as an aggregate in concrete production or for the production of frost protection layers in road construction.
Clays and loams
The clayey-sandy layers in the Geopark were formed about 25 million years ago during the Tertiary period, and later during the Elster and Saale Ice Ages. Clay has been used since the Middle Ages for the production of utility ceramics and is still mined in the Geopark, sometimes in combination with kaolin. The clay deposits in Bennewitz and Wurzen were discovered around 1830 during the construction of the Leipzig-Dresden railway. The railway and industrial pioneer Gustav Harkort used the raw material to build brickworks. Over the centuries, a diverse industry (fine ceramics, tiles, refractory products) developed around the clay and loam deposits near Grimma and Brandis. Today, modern ceramic production facilities are located in Bennewitz and Leisnig.
During the Tertiary period, around 32 million years ago, the North Sea reached the porphyry hills of the Geopark. On the coast, dying plant remains formed peat in bogs, which then developed into lignite. Lignite has been used as fuel for over 600 years. This raw material was the basis for the development of a diverse coal based chemical industry and the construction of electrical power stations in the Leipzig region. There are only small deposits of coal in the Geopark, which formed between 32 and 18 million years ago. They were mined mainly in the Wurzen-Grimma area from 1831 to around 1930.
During the Upper Cretaceous and into the Tertiary period, between 100 and 20 million years ago, the exposed porphyry rocks weathered into kaolin, the white clay. A warm and humid climate prevailed for 80 million years, as a result of which the minerals in the porphyry rocks were chemically decomposed, the iron was dissolved and the feldspar was transformed into clay minerals. Kaolin has been mined near Mügeln for over 200 years as a raw material for the ceramics and tile industry and as an additive for many other products, from paper to cosmetics. The alchemist Johann Friedrich Böttger recognised the importance of kaolin when he succeeded in producing the first European hard porcelain with Colditz kaolin in 1708, which is now world-famous as Meissen porcelain.
Volcanic porphyry rocks
The porphyritic structure (large individual crystals in a fine-grained matrix) of these rocks, also known as rhyolite, can vary greatly depending on how quickly or slowly the magma cooled. The magma originated from the Earth’s mantle at a depth of about 15 kilometres. The most striking rocks are the red-brown porphyries of the Rochlitz eruption in the southern part of the Geopark and the grey quartz porphyries of the Wurzen eruption in the north. Around 30 different types of porphyry have been identified, all of which are on display at the GeoErlebnisWerkstatt raw materials centre in Trebsen. Porphyry has been quarried here for more than 900 years. Traditionally it was used as building blocks and paving stones. Today it is used as gravel and grit for building, road and railway construction. The Rochlitz porphyry tuff is on the international „IUGS Heritage Stone“ list of significant building stones/natural stones.
Greywacke and quartzite
The approx. 500 million year old greywackes of the Collmberg (former marine deposits) are no longer quarried. Nor are the 30 million year-old Tertiary sands, the so-called freshwater quartzites near Glossen/Mügeln, in which the grains are cemented together by dissolved silica.
Captions timeline and map
– Chronological formation of the geological raw materials or treasures in the Geopark Porphyry Land
– Distribution of raw materials in the Geopark
– Video tip: 1 kilogramme of stones per hour
Captions mineral resources
- Waterworks in Canitz with organic farming on the surrounding areas Lüptitz porphyry quarry near Wurzen
- Gravel extraction near Kleinpösna in the Parthen floodplain
- Clay from the younger lignite period, a sought-after ceramic raw material for 200 years
- Lignite extraction in an underground mine near Leipnitz in the Thümmlitz Forest (1927)
- Crellenhain kaolin quarry near Mügeln
- Quartz porphyry quarry near Lüptitz