Hornfels outcrop in Obrońców Pokoju street in Karpacz

Hornfels is a rock formed from mica-schist due to the impact of hot granite magma, which burst into the rocks about 320 million years ago. The rocks were transformed along the contact line with the magma, which affected the rocks with the temperature exceeding 600˚C and also with pressure and mineral solutions. These factors made the minerals forming mica-schist melt and new minerals that replaced them produced a new type of rock – hornfels. Apart from minerals typical for mica-schist, it consisted of minerals formed under low pressure and high temperature like andalusite and cordierite (almost completely transformed into pinite), and smaller amounts of pyrite and tourmaline. The whole process took place about 8-10 km under the surface of the earth.

The subsequent processes of rock weathering, erosion and elevation led to the exposure of both the magma set as granite and the rocks into which the magma once burst on the surface of the earth. Since hornfels is a rock more resistant to weathering, it means the destructive impact of water and the atmosphere, than the neighbouring granites, mica or gneiss, it forms more protruding forms in the landscape (e.g. Śnieżka, Studniční hora, Luční hora, Kozí hřbety).
If you look carefully, you will notice the difference between the local hornfels and the one from Mt. Śnieżka or Wysoki Grzbiet

Izerski Range. The latter resembles undulating mica with elongated lenses of quartz. Sometimes even with the naked eye one can see mica flakes shining in the sun, as well as other mineral crystals. The hornfels in Karpacz looks a bit different, because the second quartz crystallization significantly covered up the features of a foliated rock and made it a massive, grey-green-blue rock that resembles serpentinite. It is difficult to see quartz lenses, which seem to be somewhat blurred.

Perhaps the additional crystallization has something to do with the fact that the rock is part of the so-called hornfels float, or clods that came off the covering rock and sank in the granite magma when it made its way through mica-schist.
It is not possible to see crystals of particular minerals that form the hornfels rock within the outcrop, as they are very tiny.

However, one can see traces of different processes that have taken place since the formation of the rock. They are mostly numerous cracks running in different directions. The fissure surfaces are sometimes smooth with shallow, elongated, parallel hollows resembling scratches. They are the traces of rock movements, or faults.

Since the rock was uncovered because of mining activities, it has been subjected to intensive weathering processes. Changeable air temperatures, wetness, frost make the rock erode. It becomes lighter in colour, it sometimes crumbles and the surface wears down. What is more, plants like lichen and trees destroy the rock, especially trees, which slot in the roots that grow and blow up the stone