Haematite, close-up. This common mineral is a variety of iron oxide (Fe2O3), mined as one of the main ores of iron. The specimen shown here has a bulbous appearance, also referred to as botryoidal (grapelike), which in mining practice is referred to as kidney ore. Here it is a dull red, known as red ochre, although haematite's colour can vary from black to red to steel grey. As well as being mined for iron, it is used industrially as a red pigment in paint, and in polishing compounds. Actual width: 18 centimetres.