The minerals that make up the oxide class include those in which oxygen is combined with one or more metals. The minerals are very diverse in their physical properties: they can be quite hard (H=9) and quite soft (H=5) and the colors can range from black to very colorful. This is all due to the abundance of oxygen in the Earth's crust and the many opportunities that exist for single oxygen ions to combine with various elements in different ways.
Within the oxide class are several minerals of great economic importance. These include the chief ores of iron, chromium, manganese, tin, and aluminum.