Quartz
Quartz is the common, hard form of silica that is abundant on Earth but rare in meteorites.
Quartz is a hard, glassy mineral made of silicon and oxygen. It is one of the commonest minerals on Earth's continents and forms most sand grains. It scratches glass, which makes it easy to recognise.
Surprisingly, quartz is rare in meteorites. Most asteroids, the Moon and Mars did not go through the long recycling of rock by water, mountain building and melting that concentrated silica in Earth's continental crust. When silica does appear in meteorites, it is more often as cristobalite or tridymite, which form at high temperatures.
Quartz is very important in craters, though. When a large meteorite strikes rock containing quartz, the shock wave leaves microscopic lines in the grains called planar deformation features. These shocked quartz grains are one of the clearest proofs that a crater was made by an impact. If a rock you have found is full of glassy quartz, it is almost certainly from Earth.
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Level: Beginner Ages 7 and up