In the beginning there was the… stone
The journey into the region’s geological past takes us more than half a billion years back. That is when sedimentary rocks were formed, but since then, they have undergone several transformations due to increased temperature and pressure. They were transformed into the most common rock in the Telč region, the gneiss.
Under elevated temperature and relatively low pressure, the gneiss partially melted – its light component entered a liquid state. That resulted in typically striped migmatites – at first sight rocks with a complex, chaotic structure.
If the melting process continues long enough, a body of tens of kilometres at length can be formed. After solidification, a mass of granite forms – the second most common rock in the Telč region. The age of granite is around 320 million years.
The formation of gneiss and granite is associated with orogenic processes. It created mountain ranges that resembled the present-day Alps or Himalayas. This type of orogeny is known as Variscan orogeny and occurred about 350-310 million years ago.
After that, the rocks were „only“ weathering. During a part of the Tertiary, a humid and warm climate prevailed, leading to mainly chemical weathering. By contrast, during the Quaternary period, the climate was also freezing and dry during the ice ages – the nature of weathering was mechanical.
In the Quaternary, the geological development of the landscape was thus completed: weathering created characteristic stone formations (e.g. Míchova skála or Roštejn), stone seas (e.g. Lhotka), the present morphology of the terrain, soils, and the youngest sediments (gravels, sands). We also include specific organogenic sediments – peat. The accumulation of plant organic matter forms them under particular conditions – peat formation is conditioned mainly by suitable subsoil and climate.
Mineral raw materials
Ore mining took place in the Telč region only to a lesser extent. Silver and non-ferrous metal ores were mined near Jezdovice, in Dobrá Voda near Mrákotín and near Dačice – Slavonice. East of Telč, more significant gold occurrences are known (Optaov, Svojkovice, Želetava, etc.). Mining of brick clay and sand and the attempts to mine graphite were also of regional importance.
Historically, mining stone and aggregates is critical as well (and it is still continuing up to this day). In the wider area around Mrákotín, various colour and structural types of granite are mined; in Vanov, rhyolite or migmatites are mined. Granites are also used for fine stone production (stairs, lining, lintels, fountains, polished slabs, etc.) and have been used in many important buildings in this country and abroad. The most famous product made of Mrákotín granite is the Mrákotín Monolith erected at Prague Castle.
Attractive minerals of Telč and its surroundings include samples of pegmatites – especially „granite“ pegmatites (Kostelní Myslová, Telč, Mrákotín, etc.) and so-called lithic pegmatites (Krasonice): smoky quartz, feldspars, elbaites, lepidolite, etc. Aesthetic examples of quartz, rock crystal and smoky quartz are known from quartz veins.
Interesting features of the Vanov gneiss are large, purple-blue grains of cordierite and large specimens of apatite. The cordierite samples are among the best in the Czech Republic. Ore minerals (sphalerite, galena, pyrite, arsenopyrite, etc.) are found on polymetallic veins, often together with quartz.
Some of the best examples of so-called uranium micas in the Czech Republic come from granite fissures in the broader surroundings of Mrákotín – torbernite and autunite.
A rarity of the peat bog at Velký pařezový rybník is the organic mineral – fichtelite, which is rarely found on pine trees and tree stumps.