Geology
The rocky base of this area is formed by metamorphic rocks of Moldanubian Zone developed by a high pressure and temperature metamorphosis. The rocky base of the river Jihlava valley is quite variable. Granulites and biotite paragneisses predominate together with serpentinites in greater masses at Mohelno and Biskoupky and some other smaller ones. Also amphibolites are represented marginally, for example near Rabštejn. Fluvial sandy gravels are at some place additionally. The subsoil is overlapped by loess and loam on plateaus and troughs occasionally.
The castle hill itself forms an edge of vast granulite mass following in the western and northern direction. It is very durable rock resisting to erosion. The river Jihlavy forms a canyon with lots of rocky outcrops, for example opposite Big Rock (Velká skála) or nearby White Rock (Bílá skála).
The castle hill is bordered by the river Jihlava on two sides. There is a deep rocky ravine with a small stream forming cascades in the lower part on the eastern side. This ravine concurrently forms geological borderline. The serpentinite mass ranging to the village Biskoupky is behind the stream. The ravine called sometimes „Templštejnská“was the important geological site of prehnite and zeolite known from the beginning of 19th century. The geological site is in bottom part of the ravine. Amphibolite and biotite rocks can be found here. We can name for example prehnite, amphibolite asbestos, talc, natrolite, sepiolite, phillipsite, analcime, chabazite, clinozoisite, pyrite and many others. Unfortunately the whole ravine is wooded now and many parts are covered by soil. Some of recent finds are deposited in mineralogical collection of museums in Znojmo and Brno.
Stone for building the castle
Stable rock enabled easy founding of the castle and enough quality material. It was a good condition for building.
The creation of granulites in high temperature and pressure determines their features. It is very hard material, abrasion resistant and homogeneous. Its low water absorption coheres with its toughness against weather and frost. It is easy splitable even into regular big pieces. That’s why it is suitable for building and it was used mainly. The main source of stones were trenches dug around or the well or cellars at the castle later. Also collecting stones from rubble fields could be the supplement. The serpentinite was used occasionally. Cobblestones could be picked up in the river Jihlava valley. Grey homogeneous limestone and whitish limestone with ochre veinlets was used as well. Different kinds of sandstone were used especially for stone segments.