Select the one substance that is not a rock.

 - Brass is made in a factory. It is a solid.
 - Dolostone is a solid. It is not a pure substance.
 - Quartzite 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.
Dolostone is a rock.
Brass is made in a factory. But all rocks are formed in nature.
So, brass is not a rock.
Quartzite is a rock.