Select the one substance that is not a mineral.

 - Native gold is a pure substance. It is not made by living things.
 - A shark's tooth is not a pure substance. It is formed in nature.
 - Potassium feldspar is a pure substance. 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.
Native gold is a mineral.
Potassium feldspar is a mineral.
A shark's tooth is not a pure substance. But all minerals are pure substances.
So, a shark's tooth is not a mineral.