The Loket Castle is situated on a strategic rocky crag above the bend in the river Ohře (Eger). The foundation of the stone castle was customarily dated to the period of reign of King Přemysl Otakar I (Ottokar I of Bohemia, 1197-1230). Nonetheless, following the discovery of a Romanesque rotunda, which, according to its architectural design, belongs among the oldest Czech structures of its kind, the foundation of the castle may be dated to an earlier period, i.e. approximately to the third quarter of the 12th century. Preserved Romanesque structures include the extremely valuable rotunda, foundations of the castle tower and foundations of the north palace. The castle more or less acquired its present appearance during an extensive reconstruction completed during the reign of Václav IV, which included, for example, the so-called "Margrave House". Additional reconstructions took place in the second half of the 15th and they mostly affected the south palace where the stately hall was built during the rule of the Schlicks, and the east palace where the Schlick archive was built. Rather unfavourable for the castle was its reconstruction into a prison, which took place in the early 19th century – most of the buildings were lowered by one floor and one of the oldest parts of the castle known as the stone room was demolished completely. In 1992, the castle returned to the possession of the town and undergone intense reconstruction.
Fig.: The Loket Castle
The area is built by the Karlovy Vary granite massif solidified in roots of the Variscan Mountains folded before about 300 million years ago. After a gradual denuding of overlying rock came granite to the earth's surface. The entire massif is composed of different types of granite rocks. The granite in Loket is one of the oldest there, and is so characteristic that it has been called Loket type granite (or granodiorite, more precisely). Typical for the rock are large crystals of potassium feldspar. In most cases these are not single crystals, but intergrowths two individuals (“twins”). The crystal intergrowths originate not accidentally, but according to the so called Carlsbad (Karlovy Vary) Law. The result is that always look the same. After weathering and disintegration of granite, the feldspar crystals, called Carlsbad twins, occur in the topsoil.
Fig.: Carlsbad twin in matrix
In 1807 described this mineralogical curiosity Johann Wolfgang Goethe in a special treatise on minerals the Karlovy Vary area. The Loket type granite can be studied directly in the castle courtyard, where is also penetrated with some fine-grained aplite dykes.
Fig.: Carlsbad twin (original drawing by J. W. Goethe)
Fig.: Aplite dyke penetrating granite