Cave pearls
Small calcite spheres formed in shallow pools.
Vislupus — CC BY-SA 4.0 · Vislupus — CC BY-SA 4.0 · Vislupus — CC BY-SA 4.0 · Vislupus — CC BY-SA 4.0
A show cave near the village of Oreshets in north-western Bulgaria, known for the unusual colour of its rock formations. Most caves have white, grey or brown formations. At Venetsa they tend to yellow, orange, pink and red, the cause being minerals dissolved in the water — iron oxides above all — colouring the calcite as it was deposited over thousands of years. The cave is equipped with walkways and lighting, and the tour inside takes about forty minutes through several chambers holding stalactites, stalagmites, columns and cave pearls — small calcite spheres formed in shallow pools. It opened to visitors in 2014 after being fitted out, making it Bulgaria's newest show cave and among its least crowded. The temperature inside is a constant ten degrees or so year round — take a jacket even in August.
Small calcite spheres formed in shallow pools.
Opened in 2014 and still among the least crowded.
Dissolved iron coloured the calcite as it formed.
Near Oreshets, north-western Bulgaria
Rainwater dissolves carbon dioxide and becomes slightly acidic, seeps through limestone and dissolves calcite from it. When a drop reaches the cave roof part of it evaporates and calcite is deposited ring by ring, so the stalactite grows from above. What falls to the floor builds the stalagmite from below. When they meet a column forms. Growth is extremely slow — fractions of a millimetre a year — which is why breaking a formation thousands of years old cannot be undone.
More than six thousand recorded, about ten of them fitted out for visitors. The most important are the nearby Magura cave with its prehistoric paintings made in bat guano, the Devetashka cave with seven openings in its roof through which shafts of light fall, and the Saeva Dupka, Bacho Kiro and Devil's Throat caves, the last with an underground river. All need a car.
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