Pohorje consists of magmatic and metamorphic rocks of different ages: the metamorphic rocks are much older, yet their age is difficult to assess, since they underwent a number of metamorphoses. The oldest rocks in the Pohorje region (as well as the entire Slovenia) are about 500 million years old. The magmatic rocks are much younger; they were created about 18 to 16 million years ago. The core of the Pohorje massif is made from magmatic rocks. The prominent one is granodiorite, which gradually transforms into porphyritic granodiorite (the general public refers to the granodiorite as granite or tonalite, and the porphyritic granodiorite as dacite) in the direction of the Northwest. In Cezlak, you can find the autochthonous Slovenian rock “čizlakit”. The metamorphic rocks envelop the magmatic rocks and are represented by augen gneiss, blestnik, amphibolite, eclogite, marble, quartzite and serpentinite, which extend mostly in the Southeast part of Pohorje. The Northwest Pohorje is made from phyllitic schist with the inserts of diabase and marbled limestone, flint and sericite phyllite with inserts of marble and quartzite, granite blestnik with transitions to gneiss and sedimentary rocks; light grey to red limestones, conglomerate, sandstone and lapor.
The porphyritic granodiorite (dacite) was created by the magma, which solidified on the surface. The hot magma and the local metamorphic rocks created new metamorphic rocks with their contact and a sudden increase in temperature: “skarn”. And in the area where dacite and skarn connect, iron ore was created. Iron ore was excavated under Mala Kopa and the Mislinja Ditch in the 18th century. The most important mining mineral was the magnetite, while the skarns hold the largest findings of garnet minerals in Slovenia. The Kope Centre presents the rocks and minerals of Pohorje.
The Pohorje metamorphic rocks are intertwined with numerous flint veins, which can be up to one metre wide. The Pohorje flint was once used as a raw material for glass, and in the simple glassworks – glažutas – they melted flint more than three centuries ago. The Pohorje glassware travelled all around Europe. Granodiorite is an important natural rock, which was used mostly for paving the streets and markets, and today it is used for building overlays, as well as manufacturing kerbs and monuments. In Josipdol, the Museum of Stonecutting, Glassmaking and Forestry of the Koroška Regional Museum presents the traditions of stonecutting, glassmaking and forestry.