Sten – Östergötland

Like several of the other stones in the stone circle, I am a loose round block of gneissic granite. Not so surprising, perhaps, because such rocks are probably Sweden's most common rock type. I myself come from Kärna mosse by Malmslätt west of Linköping in Östergötland. Or comes and comes. That's where they found me anyway. Around Malmslätt there is a glacial esker that spreads out into a plain, perhaps there was a delta there, where the ice river flowed into the sea from a tunnel under the ice sheet. That's why it's called Malmslätt, malm means "sand" in many older place names (where it doesn't really mean "ore", as in Malmberget), and several places in Central Sweden near such glacial deltas have something with "malm" in the name. So Malmslätt should mean “Sand plain”.

But actually I come from the bedrock somewhere further north, then I have been broken free from the solid bedrock by the inland ice, followed it south, ended up in the ice river when the ice sheet began to melt, tumbled around and continued with the water masses further south, until I finally landed on the bottom in the delta at Malmslätt. Dazed and giddy and worned down by the water and all the other rocks and gravel and sand that came with the ice river. That's how I got my round shape, just like my friends here in the stone circle from Uppsalaåsen or from Hörnsjö in Västerbotten.

But from the beginning I came from further north, from northern Östergötland or perhaps from Södermanland, where there are plenty of gneissic granites of my kind. They belong to the older generation of granites which have ages between 1910 and 1860 million years. No one knows exactly how old I am, but we can say approximately 1880 million years, so we are not completely wrong.

From the beginning, then, I was a piece of granite, which had been formed from a magma – a hot and glowing molten rock – that intruded the earth's crust and solidified. At that time I was speckled like a salami (“prickig korv” in Swedish), or massive as the geologists say, with different minerals scattered without any preferred orientation as differently colored millimeter-sized grains or spots. But soon after I was exposed to pressure and movement in the crust, which caused the mineral grains to align, I became striped rather than speckled. I got a gneissic structure, the geologists say. That's how I became a gneissic granite.

That kind of gneissosity can be a bit tricky, it has a certain direction, and depending on which surface you look at at a stone, you can see it very clearly, or not at all. That's how it is with me, take a look and you'll see. Seen from one side, I still look speckled, like an unaffected and undeformed granite, but if you look from another side, I'm all striped and striated like gneiss.

Geologist Åke Johansson
Swedish Museum of Natural History