Select the one substance that is not a mineral.

 - Potassium feldspar is a pure substance. It is a solid.
 - Magnetite is formed in nature. It is not made by living things.
 - Bronze is made by humans. It is a solid.
Compare the properties of each substance to the properties of minerals. Select the substance whose properties do not match those of minerals.
Potassium feldspar is a mineral.
Magnetite is a mineral.
Bronze is made by humans. But minerals are not made by living things.
So, bronze is not a mineral.