The planet with a surface that is mostly covered in volcanic rock is Venus. The harsh conditions on Venus, including extremely high temperatures and pressure, have contributed to a landscape dominated by volcanic formations. Many scientists believe that Venus is home to numerous volcanoes, some of which may still be active. The planet's surface features extensive lava plains, vast volcanic fields, and unique formations such as large shield volcanoes. The study of Venus's geology helps scientists understand volcanic activity and tectonic processes, providing insights that also inform research about Earth and other rocky planets in the solar system.