Select the one substance that is not a rock.

 - A nutshell is made by a living thing. It is not a pure substance.
 - Andesite is formed in nature. It is a solid.
 - Shale is formed in nature. It is not made by living things.
Compare the properties of each substance to the properties of rocks. Select the substance whose properties do not match those of rocks.
Shale is a rock.
Andesite is a rock.
A nutshell is made by a living thing. But rocks are not made by living things.
So, a nutshell is not a rock.