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Zbrašovské Aragonite Caves

Characteristics / Evolution of the Caves

STALACTITE, STALAGMITE AND MINERAL FILLINGS

Calcium carbonate (CaCO3), the raw material of calcite, crystallizes in three modifications:

  1. Calcite is the most common. Crystallizes in a trigonal system and forms crystals called rhombohedrons and scalenohedrons.
  2. Aragonite is a less common, high-temperature modification. It crystallizes in a rhombic system and generally forms needle-like crystals.
  3. Vaterite is a rare modification which crystallizes in a hexagonal system.

The temperature and chemical conditions of the Zbrašov Aragonite Caves and their mineral waters are sufficient for the formation of aragonite. In addition to needle-like aggregates, it also forms solid coatings in the caves.

Raft stalagmites are a phenomenon of the Zbrašov caves world. They have a characteristic conical shape and are up to several centimetres high. There is a hole in the top of the stalagmite and from the longitudinal cross-section it is apparent that the stalagmites “grew” in layers. Their central input channel cannot be proved with certainty, but their porous structure is quite distinct. There are two theories of their origin and growth. One of the theories supposes that they were formed by crystallization of calcium carbonate in places where mineral water sprung to the caves from the depths. The second one inclines towards the opinion that the stalagmites are so-called raft cones which developed on the bottom of cave lakes as accumulations of thin sinter crusts. They were primarily formed by evaporation of water on the lake surface (they were floating – therefore “rafts”). Then they were successively broken by dripping water and finally sank to the lake bottom. Their conical piles on lake bottoms were then strengthened by subsequent recrystallization. Raft stalagmites were already described in the caves around the world and the mentioned theory was applied to the Hranice Karst only when loose formations of similar shapes were discovered by divers in the depths of the Hranice Abyss.

Up to several decimetres thick coatings of the walls and ceilings together with round shapes of “doughnuts” are formed predominantly by calcite with admixture of iron oxides. These hydrothermal sinters were formed on the walls under the surface of the mineral water underground lakes.