The Kamenná slunce – Stone Suns NNM consists of a small grassy hillock which lies at around 260 metres above sea level and stands above the shallow valley of the Hnojnický potok Stream in the western section of the České středohoří Mountains PLA and in the Ústecký kraj – Ústí nad Labem Region. This hillock is a unique document of volcanic activity. In the past rock was quarried here which was then added into brick-making clay which was used in the nearby brickworks to correct its properties (the ruins of the brickworks can be seen to the west of the locality). The exposed rock face left by this quarrying provides evidence that this volcanic chimney is a former “maar” (a crater with a rim, which was produced by an explosive volcanic eruption). The “stone suns” are a geological phenomenon which can be found within this crater. The locality has been protected since 1953 and covers an area of 0.8 hectares.
On the site of the volcanic chimney we can see evidence of a former maar, which is a formation which occurs when molten magma explodes and mixes with the surrounding rocks. A funnel-shaped neck was formed by the explosion and this was then filled by the expelled volcanic materials and also by fragments released from the walls of the maar. The cold, clayey particles of the calcareous rock layers became cooling centres for their surroundings. As this rock contracted it cracked in a pattern like the sun’s rays. The underground part of the exploded volcanic neck was then exposed by the actions of water.
A number of larger or smaller “suns” with a distinct ray-like crack pattern around their cores remind us of how the whole volcanic phenomena took place. In the white-grey coloured tuffs we can find dark orange-brown cores (claystones), which form the centres of the “suns”. The cores are surrounded by radial cracks (rays of the sun), which stretch out to a circular crack where the sun is in contact with the surrounding rocks. The cores of the “suns” range in size from 0.3cm to 30cm, while the complete “suns” are between several centimetres up to nearby 1 metre in diameter.
The hillock is covered with unique steppe formations. On the parts of the hillock which were not affected by quarrying the flora reaches a rich optimum condition in late May and early June. Then we can admire the Austrian flax (Linum austriacum), St. Bernard’s lily (Anthericum liliago), the feather-grasses Stipa joannis and Stipa pulcherrima, the grape-hyacinth Muscari tenuifolium, the milk-vetch (Astragalus excapus) and the Austrian milk vetch (Astragalus austriacus).
A notable fauna of thermophilous and xerophilous invertebrates has survived on the territory of the monument. Rare insects include the grasshopper Tettigonia caudata, the ground beetles Notiophilus laticollis and Masoreus wetterhallii and the butterflies eastern baton blue (Pseudophilotes (Scolitantides) vicrama) and safflower skipper (Pyrgus carthami). Nightingales (Luscinia megarhynchos) regularly nest in the neighbouring shrub stands.
The Kamenná slunce NNM is only used for scientific and educational purposes, but it is an attractive and easily accessible locality. This has led to some “visitors” digging up the centre of the “suns” as souvenirs or for private geological collections. Weathering products are cleared from the crater walls every few years and the steppe growths are regularly maintained.