Select the one substance that is not a rock.

 - Scoria is formed in nature. It is not made by living things.
 - Sandstone is a solid. It is not a pure substance.
 - Bronze is made by humans. It is not a pure substance.
Compare the properties of each substance to the properties of rocks. Select the substance whose properties do not match those of rocks.
Sandstone is a rock.
Scoria is a rock.
Bronze is made by humans. But rocks are not made by living things.
So, bronze is not a rock.