Most substances around us are mixtures. A pure substance is composed of only one type of molecule or atom, while a mixture is composed of two or more substances that are not chemically combined. For example, air is a mixture of several gases, including nitrogen, oxygen, and argon. Seawater is a mixture of water, salt, and other minerals. And granite is a mixture of several minerals, including quartz, feldspar, and mica.

There are also a few pure substances that occur naturally, such as gold, silver, and copper. However, most of the substances we encounter in our daily lives are mixtures.