Sten – Jämtland

Me and my little friends around me come from Nordhallen's soapstone quarry northwest of Åre in Jämtland, from a collection of stones that fell down when part of the wall in the quarry collapsed. We were meant to be soapstone, which is Jämtland's landscape stone. But I, the big boulder, is rather a piece of phyllite from the edge of the quarry. However, a couple of the smaller stones consist of soapstone.

If I start with myself, the Phyllite, I began my journey as a muddy sediment that was deposited on the ocean floor perhaps 500 million years ago, and then became compressed and hardened into shale. When the mountain chain (or its predecessor, the Caledonides) was formed by the collision of Scandinavia with Greenland about 420 million years ago, I was pushed down a bit into the earth's crust and transformed into a rock called phyllite. Then I and all my rock buddies were thrust as a big sheet, called nappe, several hundred kilometers east over the older, underlying basement, ending up in Jämtland.

In a phyllite, the tiny clay mineral particles in the shale have been converted into a type of mica called muscovite. The muscovite also forms thin flakes in the rock, which in the phyllite are so small that they are not visible to the naked eye. However, they give me a slightly glossy and silky luster on the surface, as you may be able to see, unlike the uniform gray clay slate. If the mica flakes grow and become so large that you can see them with the naked eye as small silvery scales in the stone, the rock is called mica schist. Both phyllite and mica schist are very common rock types in the bedrock of the mountain range. In connection with the movements when the original mountain chain was formed, the bedrock was also folded in different ways. You can perhaps see that my upper surface is not completely flat and smooth, but a little wavy; that is because of that folding.

But a couple of my little friends here are at least partially made of soapstone. You can tell by their light color, and if you touch them, the surfaces feel almost like soap In Swedish, soapstone is called “täljsten” (carving stone) because the rock is very soft, so soft that you can carve small figures out of it with a knife. This in turn is due to the fact that it consists of very soft minerals, such as serpentine and talc. Talc is actually the softest mineral there is.

The soapstone actually has a very interesting and unusual origin. It began its history as a dark and very silicon-poor rock—geologists call such rock ultrabasic—down in the Earth's mantle, which lies beneath the Earth's crust. When Greenland collided with Scandinavia and the mountain chain, or its predecessor, formed, small pieces of such ultrabasic mantle rocks were pushed up through the earth's crust and ended up as lenses in the bedrock of the mountain chain, usually in the contact between different thrust sheets. It was in connection with this that some of the dark ultrabasites were transformed into soft and often fairly light soapstone. Perhaps this helped push them up, they behaved like soft pieces of soaps being pushed up between the other, harder rocks.

As you may understand, soapstone is not a very common rock, not even in the mountain range, but occurs only as smaller bodies and lenses. The most famous soapstone deposit is at Handöl west of Åre, closer to the Norwegian border. Soapstone is mainly mined there to make stoves from; soapstone is not only soft, but also retains heat very well, so if you cover the stove with slabs of soapstone, it will retain heat longer, even after the fire has stopped. Right now the business seems to be down, but maybe it will start again. The soapstone quarry in Nordhallen is also closed. Soapstone was mined here mostly for the production of talcum powder. From what I've heard, talcum powder is mostly used to dust babies' bottoms, but there may be other uses as well.

Geologist Åke Johansson
Swedish Museum of Natural History