* Elements are pure substances that cannot be broken down further (e.g., gold, oxygen).

* Compounds are formed when two or more elements chemically combine in a fixed ratio (e.g., water, salt).

* Mixtures are combinations of two or more substances where each substance retains its own properties.

Rocks are made up of different minerals (which are themselves compounds) and sometimes other materials like organic matter or glass. These components are not chemically bonded together in a fixed ratio, and their proportions can vary widely within a rock.

For example:

* Granite is a rock composed of quartz, feldspar, and mica.

* Sandstone is made up of sand grains (primarily quartz) cemented together.

Since rocks are combinations of different substances that are not chemically bonded, they are classified as mixtures.