Tektites

 

Tektites are a type of meteorite that was made when a bigger meteorite created such a big impact that it melted the surrounding rocks and knocked some fragments of the melted rocks back out into space. They fell back to Earth. Tektites are glassy like obsidian but the composition is not the same. See here for details. It turns out that there are only 4 areas on Earth where they can be found and that dating techniques have tied them in with nearby impact craters.