Select the one substance that is not a mineral.

 - Celestine is a solid. It is formed in nature.
 - A sunflower seed is not a pure substance. It is a solid.
 - Pyrite is a solid. It is not made by living things.
Compare the properties of each substance to the properties of minerals. Select the substance whose properties do not match those of minerals.
A sunflower seed is not a pure substance. But all minerals are pure substances.
So, a sunflower seed is not a mineral.
Pyrite is a mineral.
Celestine is a mineral.