Rocks Rock at Building Stuff STEM Challenge: Rocks are natural objects that are composed of solid crystals. Rocks are made of a mixture of minerals. Rocks have different attributes (features) that are used to describe them including their color texture, luster, and hardness. Rocks are often used to build things like walls, floors, chimneys, walkways, and fences. In this STEM Challenge, your task is to design and build something useful using rocks and cement. Good luck with this STEM Challenge.