Sten – Blekinge

I am a round, loose block of gneiss granite - i.e. granite turned gneissic - from Blekinge. So, the stone block itself is from Blekinge, from a place called Halle Håle at Hörvik on Listerlandet in western Blekinge. I came there with the ice sheet perhaps 12,000 years ago. Maybe running water was also involved in transporting me, and rounding off my forms, or it is the sea waves that did it later. From where in the solid rock that the ice cap took me from is not so easy to know, and I don't know it myself, but it was probably not that far away from where I was found. So in that case I come from the Blekinge bedrock, and I am approximately 1750 million years old.

The geologists usually call such granite in Blekinge Tving granite, after a place a little north of Karlskrona called Tving, where there is such granite. So I think I'm Tving granite. In that case, I was formed from a magma – a hot melt of rock – that pushed up in the earth's crust some 1750 million years ago. It was then that much of the bedrock in Blekinge was formed. As magma I was a bit viscous. Like syrup or so, and couldn't really make it all the way up to the surface of the earth (in that case there would have been a volcanic eruption), but solidified into hard rock several kilometers below the surface of the earth, when the various minerals that I am made of crystallized. If you look closely, you may be able to see the different colored mineral grains that I, the granite, is made up of. Mostly it's light quartz and feldspar, that's why I have such a light color, but there are also some dark dots made up of biotite (also called dark mica), and maybe also hornblende.

If you look really closely, you may be able to see that the mineral grains, at least on some surfaces, are a little elongated and flattened. This is because I was exposed to pressure and movement in the earth's crust, probably quite soon after I was formed. Maybe these movements were already going on while I was crystallizing, before I was completely solid. So the mineral grains were pulled out and flattened in the same direction, this is what is called gneissic texture, and that's why I'm called gneiss granite.

All this happened several kilometers down in the earth's crust, or perhaps rather several tens of kilometers down. Then a very long time passed when not much happened. It was dark and cold (at least compared to when I was a magma) and quite boring for several hundred million years down there in the depths. Slowly, all the mountain above me was eroded away by weather and wind, and most of all perhaps by running water or glacial ice, and I came up closer to the ground. The pressure eased, and one fine day I saw daylight for the first time. How beautiful it was! Then it got very cold, the ice sheet came and laid on top of me several times, and finally it dragged me with it and dumped me in Halle Håle, where some people came and picked me up and drove me to Stockholm and to this stone circle. So now I'm a representative here for Blekinge, even though I'm not really sure I'm from there to begin with.

Geologist Åke Johansson
Swedish Museum of Natural History