326 EXPERIMENTS RELATIVE TO METEORITES. 



.ing to an examination nuule by M. Des Cloizeaux, appear disposed in the forms 

 of the regular rliomhoidal dodecahedron, we tlien perceive the brilliant matter, 

 isolated, and, as it were, driven into the interstices, under a reticulated form. 



STOXES. FUSION. 



As meteoric stones always reach us covered with a black and vitreous crust, 

 due to a superficial fusion effected in their transit through the atmosphere, it 

 might be thought that by melting them in crucibles we shovdd obtain nothing- 

 else but this same vitreous matter ; but experiment has taught that it is quite 

 otherwise, and that these substances possess, on the contrary, a very decided 

 aptitude for crystallization. Thus, by liquefying the meteorites of more thaa 

 thirty different descents, I have always obtained masses eminently crystalline. 



If meteoriks of the common type he submitted to a temperature sutiicientlj 

 high, the mass, after fusion, is composed of a precipitate of small metallic grains dis- 

 seminated in a silicated gangue of lithoid appearance. This lithoid part itself 

 is generallv divided into crystalline substances, very distinct in form. The one 

 consists of rectangular octahedrons, much flattened, and having the form and 

 arrangement which characterize peridot., especially that which is formed in scoriae. 

 This same substance is presented under two other forms in the products of fusion.* 

 The second substance habitually presents prisms with a rectangular section, often 

 aligned parallel with one another, and having a librolamellar fracture which 

 strongly resembles that oibronzitc. Their opacity does not ordinarily permit of its 

 being decided whether they pertain to the right system of the rhoml)oidal prism 

 or to the oblique system. Yet as they are, for the most part, devoid of iron, and 

 contain scarcely more than magnesium, they must be considered as pertaining 

 not to pyroxene, but to the species enstatite. Moreover, on the product of the 

 fusi(ni of the meteorite which recently fell at Tadjera, in Algiers, numerous 

 uncolored needles are to be observed which, examined with the microscope, shovy 

 very distinct angles approaching to 87", like those which correspond to the cleav- 

 ages of enstatite, {Comptes rendus, t. Ixvi, p. 517, 1868). The chemical assay 

 of these two substances justifies the conclusion to which we are led by the orys- 

 tallographic examination. 



We have seen that the analysis of most meteorites of the common type dis- 

 closes the existence therein of at least two silicates ; the one alterable, the other 

 unalterable by acids. In the experiments of which I have just given an account 

 a parting takes place between these silicates which were originally in such inti- 

 mate intermixture that they could not be distinguished. They separate by a 

 sort of liquation, and much more distinctly than in the natural meteorite ; it is 

 thus that, under diiibrent forms, the magnesian silicates, peridot (Mg. Si.) and 

 enstatite, (Mg. Si'-.,) make their appearance. The relative proportion of peridot 

 and of enstatite, in the products of the fusion, vary much with the meteorites ; it 

 is generally the enstatite which predominates, and in a certain number, (Chan- 

 tonnay, Ensisheira, Agen, Chateau-Renard, and Vorcille,) the peridot does not 

 appeal- in distinct crystals. On the contrary, the peridot may show itself in pre- 

 dominance, as in the meteorite of New-Ooncord. The reduction of the iron, 

 Avhich was in the state of a silicate, does not appear to have had any other eflFect 

 than to auo-ment the proportion of enstatite at the expense of that of peridot, 

 without other change in the nature of the compounds. 



The situation of these two species respectively, within the mass obtained, 

 deserves attention. In general, the peridot, when it exists, forms at the surface 



* Accordincr to tlio examination wliich M. Des Cloizeaux has made, one of these forms is 

 of crystals with six faces, composed of the base P of the prism gz, and of the truncation gi ; 

 the other form is composed of the base P and of two basils, (hiaenux,) of which one phiced 

 on the obtuse angles of the primitive prism of 1 19^ 3U', pertains, by the angles, to the form 

 fli, while the other is placed ou the acute angles. 



