How is a xenocryst formed?

Answer 1

A xenocryst is a mineral crystal which is imbedded in igneous rock. The crystal is formed by exotic chemical and structural reactions in the tremendous pressure and temperature of the Earth's mantle, below the crust. The crystal is then picked up by liquid magma rock, and carried up cracks and fissures into the crust, where it solidifies into igneous rock. If the magma makes it all the way to the Earth's surface (where it is called lava), it solidifies into igneous rock either as a lava flow or a volcanic eruption. A classic example is the inclusion of xenocystic diamonds in fissures of igneous Kimberlite rock in the famous diamond mines of Africa.