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Sopky v Geoparku

Hlinky Basalt Organ

The Nature Monument called “Čedičové varhany” (“Basalt Organ”) is situated in an abandoned quarry about 1 km from the village Hlinky, on the left side of the road to Přílezy. The stone pit was opened in Tertiary lava flow on the north slope of the Hůrka Hill (817 m). In the preserved extracting wall, the excellent prismatic jointing of the basalt rock (olivine nephelinite) is developed.

The wall of the old quarry is composed from up to 6 m height vertical prisms that remind of organ whistlers. The rock columns were created by the internal tension during the contraction of cooling lava flow. The orientation of the columns is accordant to the temperature gradient, i. e. perpendicular to the cold base below and the air above.

Nephelinite is fine grained to massive effusive rock formed of microscopic minerals nepheline and pyroxene (augite). In the case of abundance of olivine, the rock is named olivine nephelinite. Olivine forms small yellow-green phenocrysts and also predominates in coarse grained inclusions of foreign rocks (xenolithes), which was wrested from the lower Earth’s crust and mantle by ascending magma. Nephelinite comes under the group of basalt volcanic rocks like the olivine basalt, which forms an independent effusion directly on the top of the nearby Hůrka Hill.

GPS position

N 50° 7.264', E 12° 54.044'