Last month GlassFacts.Info covered two of the three most common types of natural glass: obsidian (January 17) and Fulgurite (January 30). Today's fact covers the third type: tektite.
NASA defines a tektite this way: Small glassy bodies containing no crystals, composed of at least 65 percent silicon dioxide, bearing no relation to the geological formations in which they occur, and believed to be of extraterrestrial origin.
The two words you want to pay attention to in that definition are extraterrestrial and believed. Tektites are almost always found at meteor impact sites and though they are believed to be from outer space that theory has yet to be proven.
The word tektite is derived from the Greek word for molten: tektos.