česky english deutsch <<< >>>

Educational Mining Trail Přebuz

Granite Rock

Educational Mining Trail Přebuz

The rock hidden in the spruce trees directly to the left of the path to Hartelsberg Hill reveals the unique structure of tin-bearing granites.

The entire route of the Mining trail Přebuz leads on the granites that solidified below the Earth's surface in the Palaeozoic (Carboniferous), in the period when coal seems originated in surroundings of Plzeň and Kladno. The Přebuz neighbourhood belongs to classical areas where granite magma development as well as relationships between granite and tin deposits has been studied. The Přebuz granite is a part of the Karlovy Vary granite massif, which penetrates the Earth's crust in a tongue-shaped body up to 12 km thick. The massif is formed by two main granite groups. The Older Complex (called “gebirgsgranite”) is about 330 million years old, the Younger Intrusive Complex (“erzgebirgsgra­nite” or “tin granite”) around 320 million years. Younger granites contain high contents of some elements, such as lithium, fluorine and tin.

Relatively high concentrations of alkalis and fluids in granite magma before solidification contributed to the unusually high melt penetration below the then Earth's surface. This has led to the creation of unique, so-called two- and three-phase structures of rocks, which we know from elsewhere mainly from volcanic conduits. Beside the groundmass with phenocrysts of quartz and feldspar, Přebuz granites contain also significant amount of fine-grained mass, which sometimes even dominates. On the rock on the northern slope of the Čertova hora Mountain (Hartelsberg) forms this multiphase granite a sharply bounded cell of spherical shape and meter size in the relatively coarse-grained granite. Another unique phenomenon on Hartelsberg is so called layered (stratified) granite with a regular alternation of coarse and medium grained zones. This alternation was initiated by periodic states of phase imbalance of the magma after when the vapour pressure opened cracks in the roof of the magmatic reservoir.

This text was written by Petr Rojík.

The boundary of two granite types in the rock on Hartelsberg

Stratified granite on Hartelsberg

Vertical aplite dyke in granite

GPS position

N 50° 21.652', E 12° 36.060'