site 22

Where is the site located?

GPS: 49° 46′ 33.89″ N, 15° 53′ 24.80″ E

The site lies in the southeastern part of the Iron Mountains National Geopark, in the eastern extension of the granite core of the Iron Mountains, forming a rolling landscape with round elevations.

What is the geological position of the site?

The site is located in the Bohemian Massif, in the marginal area of the Central Bohemian Region which is represented by the Železné hory plutonic complex at this site. This text is therefore focused on rocks which constitute a complex magmatic body solidified at great depths. By the effect of geological processes and geological time, this body got to the proximity of the earth surface.

What happened at this site in the past?

– 360–300 million years

Carboniferous and earliest Permian times (the fifth and sixth periods of the Paleozoic era) were marked by unrest due to major orogenic processes (Variscan Orogeny). Progressive collision of two continents – Laurasia in the north and Gondwana in the south (this area lies at its margin) – created the supercontinent of Pangea. This area became a part of a large mountain range of the Variscides (Hercynides), which extended from todayʼs Spain across southern England, France and Germany, as far as to central Europe. This mountain range became a solid basement of the Bohemian Massif. The orogenic processes resulted in bending, fracturing and shifting of the existing rock masses, inducing the rise of huge volumes of hot magma. Some magma batches ascended along deep-reaching fractures and reached the earth surface. Other portions of rising magma remained under the surface and constituted large, loaf-shaped bodies.

What does the site display today?

Rocks around Srní belong to the Železné hory plutonic complex – an approximately triangular body lying among the towns of Seč in the east, Skuteč in the north and Trhová Kamenice in the south.

This site is located in the eastern part of this complex, around the termination of the Nasavrky pluton – the younger, northern segment of the complex. The Nasavrky pluton passes into the older Železné hory pluton towards the southwest in the Trhová Kamenice area.

The rock exposed here is called the Hlinsko granite by the stonemasons. In geological terms, it is fine- to medium-grained biotite to amphibole-biotite granodiorite. The rock is composed of light grains of quartz (a mineral of the oxide group) and feldspar (a mineral of the silicate group), dark grains of biotite (lustrous flaky mineral of the silicate group) and amphibole (a mineral of the silicate group). Depending on the presence of mafic (dark-coloured) minerals, two most common varieties of the rock can be distinguished: a light grey and a dark grey. The light grey type has typical bluish hues due to the presence of quartz and feldspar. Aggregates or crystals of light feldspar are occasionally found in the rock. The extracted stone displays favourable properties – a high resistance to abrasion and a low absorption capacity. As such, it is suitable for outdoor use.

What was affected by man?

The Matula Quarry was opened by Jan Rozsypal in 1903. Jiří Matula became a partner and later an owner of the quarry. At those times, the extracted material was primarily used for the production of dimension stone for city pavements, especially in Vienna. Besides paving stone, the quarry also produced garden kerbs, lining stone, ashlars, irregular building stone and hand-crushed aggregate. The introduction of electrical power in 1920s permitted the use of machinery in dimension stone production: the quarry received modern equipment including its own oil-driven power station, a compressor, a rope crane and an aggregate unit. The quarry then produced not only paving but also goods worked solely by the stonemasons, such as tombstones and monuments. The quarry often supplied stone for the regulation of the Labe (Elbe) River; this is why big, irregularly cut blocks of stone are called “labáky”.

Material extracted today is still used not only as building stone but also as decorative stone. It is appropriate for cemetery architecture (monuments and tombstones), as raw material for garden architecture (fountains, flower pots, pedestals), for road construction (kerbs, ashlars, paving stones, monoliths), and can be also used as wall linings of buildings, floors, staircases and window sills.

What was discovered?

The pit quarry provided an insight in the core of the magmatic body of the Nasavrky pluton at its eastern limit. Hitherto conducted research confirmed that granites at this site pertain to the younger stage of the intrusion (magma emplacement into host rock) penetrating with finger-like apophyses to older migmatites. The younger stage of the intrusion is finer-grained and of uniform material composition. The older intrusion is of coarser grain size and contains frequent inclusions of other rocks.

The top part of the quarry face displays typical spherical weathering of granites. Granite tectonics is also visible: the rock is transected by a more-or-less orthogonal system of joints, which were initiated at the transition between the visco-elastic state and the solid state of the rock. One set of joints is parallel to the surface, the other set is perpendicular.

As suggested by recent studies, granitic magma ascends at a rate between tenths of millimetre per year and 7 mm per year. The time needed for a granite pluton to form is thus estimated at 10–100 million years. Then, at least 10 million years must elapse before the pluton becomes exhumed by erosion (mechanical removal of rocks from the earth surface by water, wind, ice etc.).

“The Iron Mountains – a geologically significant region” project of 2014

An information panel was manufactured within the project of “The Iron Mountains – a geologically significant region”. It was erected by the road between Srní and Hlinsko, at the intersection with a local road to the Matula Hlinsko Quarry. The quarry is an active one, accessible only after a prior consent by the company operating the quarry.

Mining of granite (Archive of Městské muzeum ve Skutči)