Many weathered pebbles and fragments of obsidian somewhat resemble the tektites superficially. There is a very simple test by which you can distinguish true tektites from obsidian. If you hold a thin splinter of tektite glass in a blowpipe flame, the glass melts quietly but only with the greatest difficulty. On the contrary, when you test in the same flame the terrestrial glass, obsidian, it froths up much more easily, into a bubbly, whitish mass. Although the question of where the tektites came from is still not entirely settled, most scientists agree that all tektites did have a _common_ origin. For example, tektites from widely scattered localities on the earth’s surface show not only similar queer shapes and surface markings (technically known as “sculpturing”), but also have very much the same chemical composition and, in particular, the same content of radioactive elements. Because the tektites chemically resemble certain terrestrial rocks, scientists at first believed that some kind of earth process must have created them. One suggestion was that lightning had fused dust particles suspended in the air to form them; another, that they had come from volcanoes; still another, that the tektites were simply inclusions that had weathered out of terrestrial rocks. A few scientists once took seriously the possibility that tektites were refuse from primitive glass factories! [Illustration: Tektite vs. obsidian, after blowpipe test.] While such theories have not yet been completely discarded, most scientists now feel that the tektites had their origin somewhere outside the earth. There are several reasons for this belief. First, the shape of such unusually symmetrical forms as are found, for example, among the australites, indicates that these small bodies at one time were members of a swarm of freely-spinning liquid masses. Again, flow features observed on the surfaces of certain tektites (and the fusion crust definitely identified on one specimen) show that these bodies at some time must have traveled through the earth’s atmosphere at high velocity. If, then, the tektites were not produced by earth processes, where did they come from? According to primitive legends, they were “rocks” or “pebbles” from the moon. Indeed, one of the earliest scientific theories as to their origin (proposed by the Dutch authority Verbeek in 1897) likewise attributes them to debris jetted out from the moon. Another holds that tektites are fragments of the outermost glassy layers of some so-called “meteorite-planet,” or planets.[8] Still another idea is that tektites are what is left of a comet when it passes so close to the blazing-hot sun that the “ices” which make up most of the cometary nucleus (head) are all distilled away.