Breunnerite.
Further, from one of the Lancé stones, chloride of sodium, and from the carbonaceous meteorites, sulphates of sodium, calcium and magnesium, have been extracted by means of water.
In addition to the above, there are several compounds or mixtures of which the nature has not yet been satisfactorily ascertained.
The rarity of quartz.
30. Quartz, the most common of terrestrial minerals, is absent from the stony meteorites; but in the undissolved residue of the Toluca iron microscopic crystals have been found, some of which have important characters identical with those of quartz, while others resemble zircon. As mentioned above, free silica is present in the Breitenbach meteorite as asmanite.
The conditions under which these compounds can have been formed.
31. As to the conditions[14] under which such compounds can have been formed, we may assert that they must have been very different from those which at present obtain near the earth's surface: in fact, it is impossible to imagine that phosphorus, the metallic nickel-iron and the unstable sulphides can either have been formed, or have remained unaltered, under circumstances in which water and atmospheric air have played any prominent part. Still, what little we do know of the inner part of our globe does not shut out the possibility of the existence of similar elementary and compound bodies at great depths below the surface. Daubrée,[15] after experiment, inclines to the belief that the iron is due, in many cases at least, to reduction from an olivine rich in diferrous silicates, and this view perhaps acquires some additional probability from the fact that hydrogen and carbonic oxide are given off when meteoric iron is heated: the existence, however, of such siderolites as that of Krasnojarsk, which is rich both in metallic iron and in orthosilicate of iron and magnesium (olivine), and yet presents no traces of the intermediate metasilicate of iron and magnesium (bronzite), offers a weighty objection to the general application of this view.
Classification.
32. Meteorites may be conveniently arranged in three classes, which pass more or less gradually into each other: the first includes all those which consist mainly of iron, and have, therefore, been called by Prof. Maskelyne aero-siderites (aer, air, and sideros, iron), or, more shortly, Siderites; the second is formed by those which are composed chiefly of iron and stone, both in large proportion, and are called aero-siderolites, or, shortly, Siderolites; while those of the third class, being almost wholly of stone, are called Aerolites (aer, air, and lithos, stone).
The siderites.