Sten – Gotland

I am a block of gray Silurian limestone from Ygne kuse at Högklint south of Visby on Gotland, with an age of about 430 million years. As a result, I am the youngest stone in the stone circle, even though there are even younger rocks down in Skåne. I myself am a loose block, flat but a little rounded, so it is a bit uncertain exactly where in the solid bedrock I come from, but it is certainly from Gotland (or possibly the seabed just off Gotland). Almost all of Gotland consists of gray limestone from the Silurian period, which occurred between 440 and 420 million years ago, except down at Burgsvik in southern Gotland where there is some sandstone.

At that time, Sweden and the entire continent of Baltica – what is now the northeastern half of Europe – were close to the equator and the climate was warm. Most of Sweden was covered by a shallow sea, and in the sea there were coral reefs. Some of the limestones on Gotland consist of such fossil coral reefs, while the rest of the limestones consist of gravel and calcareous mud from dead corals and other sea-living animals that lived on or around the coral reefs, and which were collected on the seabed between the various reefs when the animals died. If you bend over and look closely, you will see that I am completely full of small fossil shells and pieces of shells. If you are interested in searching for fossils, the beaches on Gotland are among the best places in Sweden to look.

As the lime mud and shells were buried by younger sediments, they became cemented together as hard limestone. Reef limestone - the limestone formed directly from coral reefs - is the hardest and is most often found in the protruding rauks - erosion remnants - found along the coasts of Gotland. At the same time, Gotland, Sweden and all of Baltica continued their journey northward by a couple of centimeters each year, until Sweden is now approximately at 60 degrees north latitude, still slowly heading north.

Limestone on Gotland has been used as a building material since ancient times. If you travel around Gotland, you will see walls and old houses and churches built from limestone blocks everywhere. The most impressive is probably the ring wall around Visby. Even now, houses can be built from limestone. But above all, limestone is used to make cement to build with. At Nordugns in the north of Gotland and Slite on the east side of the island there are large limestone quarries for cement production. But not everyone likes that you destroy the beautiful nature to mine limestone, and the limestone mining also risks sinking the groundwater level, which is important on Gotland, where there is a shortage of potable water. So there has been a lot of discussion in recent years as to whether or not you should be allowed to continue with limestone mining on Gotland.

Geologist Åke Johansson
Swedish Museum of Natural History