On the Csódi Hill in Dunabogdány in the middle of the 19th century, a quarry, which is still in operation today, was opened. Here, Miocene dacite, about 15 million years old, is mined, in the cavities of which a diverse mineral association is precipitated from hot water solutions. The most important of these are zeolites. This mineral group is represented by three species at the site: chabazite-Ca, stilbite-Ca, and analcime. Lens-shaped phacolites, which are in fact penetration twin crystals of chabazite, are also of outstanding value by international standards.
In the picture: Chabazite-Ca (phacolite), Dunabogdány (Hungary). Image width: 14 cm. Photo by László Tóth.