Sten – Grängesberg

I am a block of magnetite iron ore from Grängesberg in southern Dalarna, south of Ludvika, a smaller copy of a similar block of iron ore that stands in Dag Hammarskiöld's meditation room in the UN building in New York. Like most other ores in Bergslagen (and also in Västerbotten and Norrbotten) I have an age of around 1900 million years. I formed in close association with the volcanism at this time in Bergslagen, although the details of my formation are still debated.

There are two important iron ore minerals, hematite and magnetite, and two kinds of iron ore, hematite iron ore and magnetite iron ore. Both hematite and magnetite are iron oxides, compounds consisting of iron and oxygen, but with different formulas; hematite has formula Fe₂O₃, and magnetite formula Fe₃O₄. It gives them different looks and characteristics. Hematite is non-magnetic and has a gray-blue metallic color, but if you grind the hematite to a fine powder, it turns a brown-red or blood-red color. Hematite iron ore is therefore also called "bloodstone ore". Magnetite is magnetic – as the name suggests – and black in colour. Magnetite iron ore is therefore also called "black ore". The iron ore in Grängesberg consists mostly of magnetite ore, but there is also some hematite ore there. If you have a magnet with you, you can test that I am magnetic, and thus consists of magnetite ore.

Iron ore mining in Grängesberg began in the 16th century, and over time Grängesberg became one of Sweden's largest and most important iron ore mines, owned by Grängesbergsbolaget. They had their own railway to transport the ore to Oxelösund, where the smelter where iron was made from the ore was located. Mining continued until 1989, when the mine was shut down. But there is still iron ore left in the rocks below, so it is not impossible that mining will be resumed at some point in the future.

Geologist Åke Johansson
Swedish Museum of Natural History