Unit Overview In Solid as a Rock: Replicating an Artifact, students explore rocks and minerals and the properties of materials. The unit begins with the storybook Gayla and Natasha’s Rocky Adventure, in which twins Gayla and Natasha living in Russia explore the field of Materials Engineering as they identify a material to replicate a petroglyph (rock carving) from their archeologist mother’s study site. Over the course of the unit, students learn how to compare and categorize different materials, differentiate between the three types of rocks, and practice the methods archaeologists use to protect and replicate their discoveries. Like Gayla and Natasha, students then follow the steps of the Engineering Design Process to imagine, plan, create, and improve their own petroglyph replicas.