* Opals are minerals: Opals are made of hydrated amorphous silica (SiO2·nH2O), which is a solid substance.

* Solutions require a solvent: A solution is a homogeneous mixture where a solute (solid, liquid, or gas) is dissolved in a solvent (usually a liquid).

* Opals don't dissolve: Opals don't dissolve in common solvents like water or acids. They can be broken down over very long periods by weathering or chemical reactions, but this is not a process of dissolving in solution.

In summary: Opals are solid minerals that exist as a distinct solid form, not as a dissolved substance in a solution.