Identifier: scienceguide7692amer (find matches)
Title: Guide leaflet
Year: 1901 (1900s)
Authors: American Museum of Natural History
Subjects: American Museum of Natural History Natural history
Publisher: New York : The Museum
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: IMLS / LSTA / METRO

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more frequently than the iron meteorites, of which 350 had been found to 1929, but only 22 seen to fall. The number of falls and finds known in 1929 was 832. The list has been considerably increased during the following four years. The American Museum Collection of meteorites (March, 1933) contained 2640 specimens, representing 569 falls and finds. Large collections of meteorites reveal that the specimens of no two falls are exactly alike in structure or composition, yet it has been observed that they may be arranged into three principal groups or kinds, as noted by MerriU namely: 1. Aerolites, or stony meteorites, consisting essentially of silicate minerals with minor amounts of the metallic alloys and sulphides. 2. Siderolites or stony-iron meteorites, consisting of an extremely variable network or sponge of metal, the interstices of which are occupied by one or more silicate minerals. 3. Siderites or iron meteorites, consisting essentially of an alloy of nickel-iron with iron phosphides and sulphides.
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Technical students of meteorites have subdivided each of these groups. The aerolites and siderites are, however, the more common kinds. When cut, polished and etched, the siderites, or iron meteorites, usually show peculiar markings of crossed lines, and thus can be easily distinguished from the terrestrial irons. Some siderites have the nickel-iron alloys arranged in the form of plates parallel with the faces of an octahedron. These lamellae may be of different degrees of thickness and composed of one, two or three kinds of metal. On etching with acid these metallic bands react unequally 16 NATURAL HISTORY and show characteristic figures known as Widmanstatten hnos. Another group of iron meteorites, composed of homogeneous masses of nickel-iron, show cleavage and lamellae parallel to the faces of a hexahedron. This is due to the twinning of a cube on an octahedral face. On etching with dilute nitric acid the structures show Neumann lines. Such forms are known as hexahedral irons. A third group of

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