How can I use meteorites to teach the rock cycle?
Meteorites show rocks that never went through Earth's rock cycle, which makes them a powerful comparison: igneous, metamorphic and breccia types exist, but formed on asteroids.
The rock cycle describes how Earth's rocks are constantly recycled by melting, weathering, erosion, burial and uplift. Meteorites give pupils a striking contrast.
Chondrites are made of material that was never melted as a whole, so they are not part of any rock cycle. They are leftovers from the first few million years of the Solar System. You can ask pupils: why can we not find rocks this old on Earth? Because Earth's rock cycle and plate tectonics have destroyed or changed them.
Other meteorites show processes that pupils recognise. Eucrites from Vesta and shergottites from Mars are igneous rocks, cooled from lava, like basalt. Equilibrated chondrites, heated inside asteroids without melting, are similar to metamorphic rocks: their crystals grew and their textures changed. Many meteorites are breccias, broken and cemented by impacts, a process related to how some sedimentary rocks form from fragments. Carbonaceous chondrites contain clays and carbonates formed by water, reminiscent of sedimentary processes.
Meteorites also join Earth's rock cycle once they land. Weathering turns metal to rust and breaks the stone down, and a few ancient fossil meteorites have been found in limestone.
A useful task is to give pupils cards describing meteorite types and ask them to place each on a rock cycle diagram, explaining what process formed it and how it differs from an Earth rock.