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My second and third graders are currently working on a rocks and mineral unit. We've had so much fun exploring the properties of rocks and minerals, even once dissecting a chocolate chip cookie to demonstrate how a rock is made up of different minerals. Anyone with a little knowledge on rocks knows how pumice might fit into this unit, but popcorn? Who knew! We took two rocks, pumice and obsidian, made from the same material (in this case cooled lava) and compared them. We took notes on their characteristics, measured each rock, and tested their density in a cup of water. Pumice (when not water-logged as some of my third rotation discovered :/) actually floats, while obsidian, like typical rocks, sinks. How is it possible to have two items made from the same material? To explain, I brought out un-popped corn kernels and popcorn. They repeated their exploration on these two items, also both made from the same material. Would the results be similar? Yes. Popped corn is similar to pumice. Kernels are similar to obsidian. The air and heat combined with the original material in both sets of items creates a change in shape, size, texture, color, volume, and density. Pretty cool! For being serious scientists and not eating any of the test materials, I rewarded each group with a small bowl of fresh popcorn to sample. I told them there was a possibility of earning this treat up front. Otherwise it would be pure torture to engage four senses for an entire lesson without enjoying a little taste (if desired) at the end.