Metals in the Earth's crust
Almost all the metals we use come out of the ground. A mineral is a naturally occurring solid substance with a definite chemical make-up, found in the rocks of the Earth's crust. Most metals do not occur as pure elements; instead they are locked up chemically, usually as oxides, carbonates or sulphides.
Key idea
A mineral is a natural solid with a fixed composition. An ore is a rock or mineral that contains enough metal to make extraction worthwhile.
From mineral to ore
Not every mineral is worth mining. When a mineral holds a large enough proportion of a useful metal to be extracted at a profit, we call it an ore. For example, haematite is an iron ore (iron(III) oxide), bauxite is an aluminium ore, and malachite is a copper ore (a copper carbonate). A few very unreactive metals, such as gold, are found native — as the pure metal — because they do not easily combine with other elements.
Example
Haematite contains iron combined with oxygen as iron(III) oxide, Fe₂O₃. To obtain the metal, the iron must be chemically separated from the oxygen.
Why the form matters
The way a metal is combined in its ore decides how it is extracted. Metals joined to oxygen (oxides) are usually freed by reduction — removing the oxygen. The more reactive the metal, the more strongly it is bonded, and the harder and more costly the extraction becomes.
Remember
- Mineral = natural solid with fixed composition.
- Ore = mineral with enough metal to extract economically.
- Unreactive metals (e.g. gold) can be found native as the pure metal.