Select the one substance that is not a rock.
Wool is made by living things. It is not a pure substance. Scoria is formed in nature. It is a solid. Obsidian is a solid. It is formed in nature.
Rocks are made of minerals. Here are some properties of rocks:
They are solid.
They are formed in nature.
They are not made by living things.
They are not pure substances.
Compare the properties of each substance to the properties of rocks. Select the substance whose properties do not match those of rocks.
Obsidian is a rock.
Scoria is a rock.
Wool is made by living things. But rocks are not made by living things.
So, wool is not a rock.