JULIEN, GENESIS OF ANTIGORITE AND TALC 29 



even though quite free from the mineralizers, etc., characteristic of that 

 process. It consists of a crystalline aggregate of olivine and antigorite — 

 the latter designated as "primary," i. e., of supposed contemporaneous 

 intergrowth with the olivine. 



All the foregoing forms of the hypothesis of limitation of antigo rite- 

 genesis to a deep-seated zone are, in my Judgment, controverted by in- 

 ternal evidence, the common survival of deweylite in the chemical compo- 

 sition and the common association of chrysotile, each with a genetic his- 

 tory essentially connected with lateritic decay. 



Not having yet found any analyses of "^stubachite," we have at least the 

 evidence that it is accompanied by an abundance of chiysotile, together 

 with "schweizerite," a substance shown by its analyses to consist of a mix- 

 ture of massive antigorite, chrysotile and nemalite. "Stubachite" there- 

 fore appears to pertain to a peridotite (dunite) once partly saturated 

 with deweylite, brucite and sepiolite in the belt of weathering, which have 

 been later converted respectively into crystalline antigorite, chrysotile and 

 talc, at a temperature far less than that attending pneumatolytic action. 



DIRECT HYDRATION BY AGENCIES WITHIN TWO BELTS 



On account of the strong alliance, rightly suspected, of the associations 

 and characteristics of antigorite with the processes and products both of 

 the belt of weathering and of a more deep-seated region, other writers 

 would embrace a broader zone as the location for conversion of olivine 

 directly into antigorite. As this has been expressed by A^an Hise •}* 



"Serpentine is a product of the zone of katamorpliism, including both the 

 belt of cementation and the belt of weathering." 



In these hypotheses, the dual character is applied only to the locations 

 and the range of conditions considered requisite for completion of a single 

 process for derivation of antigorite directly from olivine. This is shown 

 by the fact that, in every case, a single equation suffices these authors to 

 explain the supposed reactions. There is a general vagueness concerning 

 the actual process, but no questioning of its essential unity of reaction. 



For the above view, based upon the apparent simplicity of direct addi- 

 tion of water and oxygen to produce antigorite. the following reactions, 

 among others, have been suggested by Van Hise:^^ 



3 Mg^Fe^SijOg + 4 H,0 + 2 = 2 H.MgaSi A+ 2 FegO, + 2 SiO, 

 Olivine '•Serpentine " Magnetite Quartz 



" Op. cit., p. .S49. 

 Op cit., p. 310. 



15 



