Rock Cycle Study Guide Vocabulary Words Rock Cycle – the process that recycles rocks into other kinds of rocks Rock Key – a classification system for identifying unknown rocks Igneous Rock – a rock that is created after lava or magma (melted rock) cools and hardens Sedimentary Rock – a rock that forms when sediments press together Metamorphic Rock – a rock that has been changed by heat or pressure Hardness – the test of how easily one rock will scratch (or be scratched) by another object Luster – the shine of a rock Streak – the mark left by a rock when rubbed on a plate Cleavage – the smooth break in a rock Fracture – the rough break in a rock Characteristics of Rocks Igneous Metamorphic Sedimentary Forms when lava (magma) cools and hardens Can have crystals, Rocks that have been changed from heat and pressure You can Formed when small pieces of rock are pressed together You can