General Characteristics

County (administration): South Bohemia Region
District (town): Strakonice
Cadastre: Zálesí u Drážova
Map 1 : 50 000 (sheet No): 2234, 22341
Geological region: Šumava Moldanubicum - district KT; Moldanubicum of the Český les Mts.; Domažlice crystalline complex; W-Bohemian Pluton; W-Bohemian basic magmatites
Accessibility: - passable footpath
Excursion locality: yes
ID : 4233

Geology

Short characteristics of the site: "Near the solitude of Růždí in the valley of the Růžďský brook, you can come across a huge monolith, the shape of which resembles a blacksmith's anvil. According to legend, the giants from the Giant Castle forged it. ”So many quotes from the portal www.mapy.cz. The mentioned monolith is a part of outcrops and free blocks of syenite porphyry. Massive log cabins and blocks are up to 5 m large and intrude in a length of about 60 m, their outcrops form a rocky threshold in the creek, 100 m below which is the old mill Růždí, there is a well near it. From the road to Maleč, a green tourist sign leads here from the solitude of U Biskupa, which continues through the forest to the settlement of U Benedy, where the asphalt road continues from Kváskovice. The blocks are at the point where a 20–30 m thick vein of syenite porphyry runs in the direction of 80 °, which pierces the discordantly foliated biotite orthogneiss. Very massive and tough rock is randomly oriented. Porphyry is atypical, darker than the usual type with a fine-grained base and with irregularly interspersed sporadic phenocrysts of potassium feldspar up to 1 cm, phlogopite accumulations reach 4 mm. The cracking is sparse into large blocks, one of which forms said anvil. The rock composition is K-feldspar 35%, plagioclase 30% phlogopite 20%, pseudomorphisms after ortopyroxene and / or olivine 10%, clinopyroxene 2%. As an accessory, long prismatic apatite and zircon are very abundant, ilmenite is rare, xenomorphic pyrite is abundant, rarely with the inclusion of chalcopyrite. Secondary is actinolite, serpentine minerals and fine-grained talc. K-feldspar forms idiomorphic growths up to 5 mm, and is also in the matrix together with plagioclase. Gamma spectrometrically determined contents of natural radioactive elements, especially uranium, are high (average of 2 measurements): K = 4.9%, eU = 17.5 ppm, eTh = 33.7 ppm, magnetic susceptibility varies in the range of 0.18–0,24 x 10-3.
Regional geologic unit: Bohemian Massif - crystalline complex and pre-Variscian Palaeozoic - Moldanubicum - Magmatites in Moldanubicum
Stratigraphy: variské (hercynské) stáří vyvřelin
Subject: geology, geomorphology, petrology
Geological phenomenon: characteristic rock, rock plate, frost cliff
Genesis: magmatic
Rock: porphyry

Territorial conservation

Level of protection: Registered interesting geological localities
Protection of a geol. phenomenon: C - Geological phenomenon is the reason for a registration in the database of CGS
Conflicts of interests: without conflicts

References

Žáček, V. et al. (2021): Vysvětlivky k základní geologické mapě České republiky 22-341, list Vacov. - Archiv České geologické služby, Praha.

Elaboration and Updating

Elaborated by: Žáček Vladimír, 20.01.21

Citation

The database Significant geological localities of the Czech Republic: 4233 [online]. Prague: Czech Geological Survey, 1998 [cit. 2024-04-28]. Available from: http:// lokality.geology.cz/4233.

Location in map: