Tektite

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Tektites (from Ancient Greek τηκτός (tēktós) 'molten') are gravel-sized bodies composed of black, green, brown or grey natural glass formed from terrestrial debris ejected during meteorite impacts. The term was coined by Austrian geologist Franz Eduard Suess. They generally range in size from millimetres to centimetres. Millimetre-scale tektites are known as microtektites. Tektites are characterized by: a fairly homogeneous composition an extremely low content of water and other volatiles an abundance of lechatelierite a general lack of microscopic crystals known as microlites no chemical relationship to the local bedrock or local sediments distribution within geographically extensive strewn fields

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