Select the one substance that is not a mineral.

 - A turtle shell is not a pure substance. It is made by a living thing.
 - Celestine is a pure substance. It is a solid.
 - Hematite is not made by living things. 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.
A turtle shell is made by a living thing. But minerals are not made by living things.
A turtle shell is not a pure substance. But all minerals are pure substances.
So, a turtle shell is not a mineral.
Celestine is a mineral.
Hematite is a mineral.