I believe the answer is
naturally occurring minerals
metal alloys
The metal alloy is a solid solution that made of metal and other elements.
The example of an alloy is bronze, which is made of copper mixed with nickel, aluminum, zinc or manganese. Most minerals should form a solid solution too, but not all of them.Gases present in air is not solid at all. A solution of HCl and sugar will not form solid solution either.
