Select the one substance that is not a mineral.

 - Native gold is a solid. It is a pure substance.
 - A turtle shell is made by a living thing. It is a solid.
 - Magnetite is a pure substance. It is formed in nature.
Compare the properties of each substance to the properties of minerals. Select the substance whose properties do not match those of minerals.
A turtle shell is made by a living thing. But minerals are not made by living things.
So, a turtle shell is not a mineral.
Native gold is a mineral.
Magnetite is a mineral.