IGNEOUS ROCKS METAMORPHIC ROCKS The Rock Cycle Magma inside the earth solidifies slowly creating MELTING & SOLIFIFICATION INTRUSIVE igneous rocks. Extreme heat and pressure can cause one type of rock (limestone is a sedimentary rock) to turn into another type of rock (marble is metamorphic). The limestone NEVER melts, it is changed simply from heat and pressure. Lava solidifies quickly at the surface resulting in EXTRUSIVE igneous rocks. SEDIMENTARY ROCKS The weathering and erosion cause pieces of IGNEOUS AND METAMORPHIC rocks to break apart into smaller debris. Larger pieces of rock will form conglomerate and breccia, smaller pieces of debris and mud will form sandstone, shale, and mudstone. This is cementation. Other sedimentary rocks were formed from buried layers of plants. Coal is a sedimentary rock formed from millions of years of layers of dead plant being compacted to form the biological sedimentary rock.