Lithologies of Catalonia

A sedimentary rock made essentially of calcium carbonate. It is the karst rock par excellence: slightly acidic water dissolves it, carving out caves, potholes and galleries. In Catalonia it underlies the great majority of cavities.

A detrital sedimentary rock made of rounded pebbles cemented in a matrix. Where the cement is calcareous, a distinctive karst of caves and tafoni develops, as at Montserrat or Sant Llorenç del Munt.

A magnesium-rich carbonate rock related to limestone but more resistant. It dissolves more slowly and tends to produce rugged karst forms with sturdy galleries.

A sedimentary rock of cemented sand grains. It is only slightly soluble, so mechanically formed cavities — rock shelters, overhangs and erosion caves — predominate over classic dissolution karst.

An intrusive igneous rock, hard and crystalline. It does not dissolve: its cavities are granitic caves formed by erosion and the shifting of blocks (block caves and tafoni).

A carbonate rock that precipitates from calcium-rich waters, often at springs and waterfalls. It can encase cavities and form tufa caves, as in the area around Banyoles.

Highly soluble calcium sulphate. It generates a fast, active karst, with sinkholes and caves that can evolve within a short geological time.

A sedimentary rock intermediate between clay and limestone. It is not favourable to large cavities and often acts as an impermeable layer that governs drainage in the surrounding karst.

Limestone recrystallised by metamorphism. It retains the solubility of carbonate, so karst can also develop in it, often producing clean, polished galleries.

A foliated, insoluble metamorphic rock. Cavities are scarce and tend to be linked to fractures or to contact with carbonate rocks.

A fine-grained metamorphic rock derived from clays. Impermeable and insoluble, it rarely hosts cavities of any notable size.

A very fine-grained, plastic sediment. It acts as an impermeable layer; the few associated cavities are usually conduits in soft materials or infill within other caves.

An extremely soluble evaporite rock. It forms one of the fastest karsts that exist, as at the Cardona salt diapir, with caves that change from one year to the next.

An effusive volcanic rock. Its cavities are lava tubes and bubbles linked to volcanism, not dissolution karst.

An unconsolidated detrital sediment. It does not form karst; its cavities are short-lived and linked to erosion or collapse processes.