Tektite

Tektites (from Greek τεκτός tektos, molten) are gravel-size bodies that are composed of black, green, brown or gray, natural glass that are formed from terrestrial debris ejected during extraterrestrial impacts. They are characterized by 1. a fairly homogeneous composition; 2. an extremely low content of water and other volatiles; 3. an abundant lechatelierite; 4. a general lack of microscopic crystals known as microlites and chemical relation to the local bedrock or local sediments; and 5. their distribution within geographically extensive strewnfields. Tektites generally range in size from centimeters to millimeters. Millimeters-size tektites are known as microtektites.