Ruby in Kyanite palmstones

Kyanite is a mineral found mainly in metamorphic rocks. It most often forms from the high-pressure alteration of clay minerals during the metamorphism of sedimentary rocks.

Corundum, (sapphire and ruby) forms deep in the Earth's crust and is brought to the surface in igneous rocks that are high in aluminium but low in silicon, such as basalts. Corundum is also found in rocks that have been metamorphosed.