307. Aerolites.—There is no certain evidence that any deposit from ordinary shooting-stars ever reaches the surface of the earth; though a peculiar dust has been found in certain localities, which has been supposed to be of meteoric origin, and which has been called meteoric dust. But solid bodies occasionally descend to the earth from beyond our atmosphere. These generally penetrate a foot or more into the earth, and, if picked up soon after their fall, are found to be warm, and sometimes even hot. These bodies are called aerolites. When they have a stony appearance, and contain but little iron, they are called meteoric stones; when they have a metallic appearance, and are composed largely of iron, they are called meteoric iron.
There are eighteen well-authenticated cases in which aerolites have fallen in the United States during the last sixty years, and their aggregate weight is twelve hundred and fifty pounds. The entire number of known aerolites the date of whose fall is well determined is two hundred and sixty-one. There are also on record seventy-four cases of which the date is more or less uncertain. There have also been found eighty-six masses, which, from their peculiar composition, are believed to be aerolites, though their fall was not seen. The weight of these masses varies from a few pounds to several tons. The entire number of aerolites of which we have any knowledge is therefore about four hundred and twenty.
Aerolites are composed of the same elementary substances as occur in terrestrial minerals, not a single new element having been found in their analysis. Of the sixty or more elements now recognized by chemists, about twenty have been found in aerolites.
While aerolites contain no new elements, their appearance is quite peculiar; and the compounds found in them are so peculiar as to enable us by chemical analysis to distinguish an aerolite from any terrestrial substance.
Iron ores are very abundant in nature, but iron in the metallic state is exceedingly rare. Now, aerolites invariably contain metallic iron, sometimes from ninety to ninety-six per cent. This iron is malleable, and may be readily worked into cutting instruments. It always contains eight or ten per cent of nickel, together with small quantities of cobalt, copper, tin, and chromium. This composition has never been found in any terrestrial mineral. Aerolites also contain, usually in small amount, a compound of iron, nickel, and phosphorus, which has never been found elsewhere.
Meteorites often present the appearance of having been fused on the surface to a slight depth, and meteoric iron is found to have a peculiar crystalline structure. The external appearance of a piece of meteoric iron found near Lockport, N.Y., is shown in Fig. 350. Fig. 351 shows the peculiar internal structure of meteoric iron.
Fig. 350.
Fig. 351.