JULIEN, GENE.Sh^ OF ANTIGORITE AND TALC 37 



10 



According to a view now in common acceptation, 



■"the conception of G. I'. Merrill, that 'the formation of serpentine as a rock is 

 a deep-seated process.' however, does not preclude the generation of dissemi- 

 nated serpentine, regarded not as a rock but as a mineral species, within the 

 belt of weathering. . . . The probable reaction is as follows : 



2 MgjSiO.-f 2 H,0-l-CO, = Mg3H,SiA + MgC03" 



Olivine Serpentine JIagnesite 



With certain variations in detail, the same hypothesis of direct produc- 

 tion of antigorite by weathering has been favored by G. H. 0. Volger in 

 1855, A. D'Achiardi in 1874, F. Becke in part in 1878, J. D. Dana in 1883, 

 H. Eosenbusch in 1892, T. G. Bonney and i'. A. Raisin in 1904, G. Piolti 

 and K. A. Eedlich in 1908. F. Cornu in 1905 has even pointed out the 

 ' passage of olivine into antigorite only on the rainy sides of the basalt 

 peaks of the Bohemian Mittelgebirge. R. Brauns^^ in particular has 

 maintained a similar view, with the addition that the antigorite formed 

 during weathering has been at the same time further altered into "web- 

 skyite" — 1 volume of the former into 1.61 volumes of the latter. As I 

 Und, by recasting of his analysis, "webskyite," with its supposed formula 

 HgR^SigOja -|- 6 aq., to be merely an impure aggregate of deweylite and 

 hyalite, Brauns has thus unconsciously approached the fact that deweylite 

 is an immediate and essential product of decay of olivine by weathering. 



In his study of the decay of a serpentine rock of Bohemia by weather- 

 ing, a still closer approach to discovery of the genesis of antigorite was 

 made by A. Schrauf :^^ 



"In the magnesite originating from serpentine, a magnesia h.vdrosilicate 

 forms a never-failing constituent." 



This he separated through removal of the magnesium carbonate by 

 "digestion in acetic acid. On analysis of the residue from drying at 130° 

 C, he found the figures to correspond in molecular ratios to those of 

 antigorite, H^MggSioOg, in predominance, though leaving 4 per cent, of 

 '''free or hygroscopic water" ! This appears to be almost the only instance 

 ■on record of claimed detection of antigorite among the products of rock 

 decay. As it happened, by that 4 per cent, apparently of superfluous but 

 actually of combined water, he missed the identification of the real hydro- 

 silicate present. An easy recasting of his analysis, on the basis of the 



1" F. W. Clarke : The Data of Geochemistry, 575, U. S. Geol. Surv. Bull. 491. Wash- 

 ington, 1911. 



" N. .Thrb. f. Mln., Bell.-Bd. V, 318-324. 1887. 

 i-'Zts. f. Kryst. u. Mln., VI, 349, 1882. 



