Surely this is one of the stranger things found in our universe recently. LINK This planet is tidally locked, so only one side faces its star (like only one side of our moon ever faces Earth). And, it's so close to its star that the heat vaporizes rock. The opposite side is constantly exposed to space, so it is incredibly cold at -330F. Then, there is a wind of 3,000mph that carries the vaporized rock clouds from once side to the super cold other side, where the heat change condenses the vaporized rock to form LAVA RAIN!! The lava is added to a lava ocean that then flows to the hot side to be vaporized again!! It sounds similar to our water cycle - only with rock!!
'Rock' is just a combination of elements that are frozen, ie sitting in the local environment at temperatures that are less than their boiling point. In essence the planet is just doing what Earth and every or orbiting body tries to do - reach thermal equilibrium by distributing heat evenly across its entire surface. It's just doing it at a higher overall temperature - with more graphic results.