Karkonosze granite

Granite is a type of intrusive rock, i.e. rock formed in the deeper parts of the earth’s crust from magma that cooled and solidified. The slow process made granite crystals quite huge and they can be seen with the naked eye. The main components of granite are: quartz (grey, partly transparent crystals), feldspars (pink and white opaque crystals) and biotite (tiny, shiny, black plates resembling pepper scattered all over the rock).
Depending on the crystal size, there are a few types of granite found in the Karkonosze Mountains. The specimen on the left is fine-grained granite while the one on the right is medium-grained.
In the first specimen there are elongated groups of large minerals called pegmatites, in the upper and lower part of the left lateral side. They are formed from unusually large rock-building mineral crystals. Here, they are mostly dark pink feldspar crystals with grey, glassy quartz crystals and dark biotite crystals, up to 2 cm long. A similar pegmatite group is on the left side of the block. A small pegmatite group can also be seen in the lower part of the right side of the block. On the walls of the medium-grained granite there are considerable mineral crystals, the same as those forming the neighbouring fine-grained block. The feldspars are 4-5 cm large and some of the pink feldspars have got white rims. The grey and glassy quartz crystals are small and similar to even smaller biotite flakes scattered throughout the rock.

The Karkonosze granite was formed about 320 million years ago at a depth of 8-10 km. As the earth’s crust was uplifted, the granite emerged onto the surface of the earth.

Both specimens come from the mine in Szklarska Poręba Huta (Jizera Mountains).