The rarest gemstone in the world is considered to be a transparent mineral of reddish ... formed deep underground in a pegmatite — an igneous rock. Its chemical formula is Bi³⁺Sb⁵⁺O₄ ...

Igneous intrusions are a type of rock feature. They form when molten rock cools below the surface of the Earth. Join Isla and Connor as they explore igneous rock landscape features at Traprain Law ...