a form of natural glass formed during meteorite impacts. The approaching meteorite fused silicates in the ground below int glass vapour and sends it into the atmosphere. it condenses and falls back to earth again as glass droplets.
My favourite tektites are found in fish fossils in the Yucatan peninsular. The fish gills have been clogged with micro tektites. The tektites were formed during the meteorite impact which caused the end Cretaceous mass extinction. this means it is possible to date the demise of the fossilised fish to one very specific day in history -- the day the meteorite hit and the world ended for most of the dinosaurs.