Page:Popular Science Monthly Volume 7.djvu/612

594 These meteorites are exceedingly tough, so that it is difficult to break them up; this is due to the iron grains being partly connected by fibres and folia. Still, the nickeliferous iron is present in detached masses, or occurs sporadically in the stone. Hence these meteorites belong to the great class of Sporadosidères of Daubrée. In this class Daubrée distinguishes three species: those containing much, little, or but very little iron, so that it can only be recognized by a magnifier or a microscope; these species he designates as Poly-, Oligo-, and Krypto-Sporadosidères. Accordingly, the Iowa County meteorites are Oligo-Sporadosidères, that is, meteoric stones containing but little plainly visible metallic iron, in detached grains. I find that these stones contain seven per cent., by weight, of metallic iron. The specific gravity of these meteorites is, therefore, rather low, namely 3.57.

The fracture is very rough and uneven, showing the lustrous metallic iron, and also irregularly rounded spots of lighter gray to white on the dark-gray ground. These rounded stony concretions show very well on a ground surface of the stone; they have given rise to the name Chondrites, introduced by G. Rose, for this class of meteorites. I find that the grains of lighter color contain less of iron silicate, but otherwise are composed of the same minerals.

These minerals are essentially two, namely, Olivine, which is soluble in muriatic acid, and Pyroxene, which is not soluble in this acid.

Besides, the stone contains some troilite, that is, iron sulphide. The following table gives the mineralogical composition of the Iowa County meteorites, according to a number of analyses:

The olivine is the variety known as Hyalosiderite, which contains two atoms of magnesium to each atom of iron. In the pyroxene of these meteorites the same ratio of iron and magnesium obtains; hence this variety is Hypersthene.

The following table gives the result of my analyses of the average composition of the Iowa County meteorites: