Sun stone (heliolite) is a plagioclase feldspar mineral with the inclusion of other minerals - hematite and goethite, which are included in the composition of spar in the form of small regularly oriented flakes. As a result, reflections of different colors of the rainbow are observed in sunlight in a sunstone with a certain orientation to the light.
You can see sun-stone stone for sale and buy it in the Minerals of Russia online store.