Lake limestone and mudstone

A mudstone layer crosses the lake origin limestone. The circle piece for scale purpose measures 6 cm diameter. Iron oxides discolor the limestone surface to ochre. Limestones of lake origin in Bages contain really small grains coming from the mud in lake beds. Most of the calcium carbonate comes from charophyta freshwater algae, exoskeleton of small ostracode crustaceae (from 0,4 to millimeters length) and snails shells. These rocks are dark gray after their content of organic matter. The lake origin limestones are were used in walls, mainly in the norh of the Bages district. Nowadays, lake origin limestones are extracted and ground for the manufacture of concrete and basic components of construction.

Limestone is a calcareous rock made of mainly calcium carbonate. The most frequent limestones in Bages are arranged in really resistant to the erosion layers. They come either frommarine or lake origin, as the one in picture. Nowadays limestones are mined in quarries as a material for building while, in the past they were used to obtain lime. Marine limestones of Bages contain a lot of macrofossils because they were sourced in reefs.

Massive limestone breaks in shell like shape. This pattern is repeated in most of fine grain, homogeneous rocks as chert and obsidian -a natural glass. Artificial glasses break in shell shape as well; it is obvious at the bottoms of champagne bottles.

[photo Florenci Vallès]