- Aluminum is a kind of metal
- Iron is a kind of metal
- Therefore, iron and aluminum are kinds of metal

- Iron and aluminum are kinds of metal
- Rocks often contain large amounts of metal
- So, rocks may contain large amounts of iron and aluminum

Therefore, rocks may contain large amounts of iron and aluminum
Question
Large amounts of metals like iron and aluminum are found in

Context
- Rocks often contain large amounts of metal 
- Aluminum is a kind of metal 
- Iron is a kind of metal