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Tachovská rokle

The ravine Tachovská rokle lies in the crystalline units of Český les, represented by migmatitized cordierite paragneisses of Moldanubicum and by the Bor granite massif. The belt formed by biotitie paragneisses with sillimanite, quartzites, graphite gneisses, amphibolites, serpentinites, limestones and erlans markedly widens in area of Tachov. A distinct quartz vein goes through the crystalline rocks. It belongs to the quartz-vein complex of the so-called Bohemian quartz wall.

The first locality is in the slope of Tachovská rokle in place, where off-road motorcycle racing used to happen. In an eroded groove in the former raceway are exposed bare outcrops of a pegmatite vein in a migmatized sillimanite-biotite paragneiss. In small cavities in coarse-grained pegmatite domains consisting of beige orthoclase, gray quartz and chloritized biotite was found light beige, imperfectly crystallized prehnite. The size of prehnite crystals is up to 3 mm, the largest cavity, prevalently filled by prehnite, has 2 cm in size.

The second locality is represented by serpentinite outcrops in place, where stands an old starting tower for motorcycle racings. The serpentinite is penetrated by veinlets of chrysotile asbestos with thickness up to 5 mm. Red garnets occur rarely. Serpentinite and garnets were formerly grinded and used for decorative objects. Another finding place on the forest rim bellow a gardening settlement affords reniform nodules of limonite and yellow-brown opal to chert, which were formerly used for fabrication of decorations too. In the field, west of the Tachovská rokle, a marked tectonic dislocation in NW-SE direction passes, on which a mighty quartz vein evolved. After plowing quartz crystals can be found, some of which approach up to the rock crystal.

GPS position

N 49° 48.020', E 13° 37.240'