Roseberry Topping is an amazingly shaped hill that overlooks Middlesbrough and Teesside. The crag on the end was formed when the end of the hill collapsed in 1912. This was because they were mining underneath. If you look carefully at the bottom picture you will see that there are thin layers of shale dividing up the sandstone. The shale is very weak - you can pull it out with your fingers. No wonder the rock collapsed. They were mining for iron ore. There are rust coloured deposits in the second picture. The iron ore was taken to Teesside where it was smelted in blast furnaces. Smelting works because carbon is more reactive than iron. Reactivity in metals is to do with how easily they can lose electrons. The Group 1 metals like potassium and sodium lose their outer electron very easily so they are the most reactive. They are more reactive than carbon so they can't be smelted. They have to be extracted by electrolysis which is expensive. The more stages in the extraction process, the more expensive the metal.
