A complex alkali rich inosilicate mineral (it contains varying amounts of sodium, potassium and calcium). It is a product of contact metamorphism and formed when an alkaline syenite intruded into limestone. The resultant charoite is formed by metasomatic processes. Hot alkaline rich fluids circulate through the rock at relatively low pressure as the intrusion cools. Over time the original minerals which formed the rock dissolve and are replaced with new minerals. The composition of these minerals is determined by the composition of the fluid.
Charoite very much is a mineral and not a rock. However, minerals generally do not form in isolation and are part of a more complex process which usually results in an assemblage of associated minerals. Charoite samples often contain white orthoclase feldspar and the pyroxene Augerine, as well as a variety of other much rarer alkaline minerals. Charoite is usually fibrous and this tends to make samples chatoyant (they seem to shimmer when moved under the light).
Charoite has only been reliably reported from sites in Northern Russia. All of these sites are part of a massive alkaline igneous province.