Select the one substance that is not a mineral.
A: Hornblende is a pure substance. It is not made by living things.
B: Fluorite is a solid. It is formed in nature.
C: A turtle shell is made by a living thing. It is not a pure substance.
Compare the properties of each substance to the properties of minerals. Select the substance whose properties do not match those of minerals.
Fluorite is a mineral.
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.
Hornblende is a mineral.