JVLIEV, 0EME818 OF ANTIGORITE A:ND TALC 35 



The office of deweylite has not ever been recognized, doubtless in part 

 on account of the difficulty of detection of a colloidal amorphous sub- 

 stance, and in part of its general alteration into antigorite. Evidence 

 of the latter change is revealed by the frequent partial survival of dewey- 

 lite grains in intermixture, and also by the very chemical composition of 

 many specimens of antigorite. , 



For example, T. S. Hunt made among others the following analysis'^ 



of chrysotile 



"from a narrow vein traversing the Eozoon rock of Petite Nation seignory, 

 Quebec : silica, 43.65 ; magnesia, 41.67 ; protoxyd of iron, 1.46 ; water, 13.48 ; 

 100. 16." 



He commented thus, with surprise, on his results : 



"these serpentines from the Laurentian limestones are remarkable for their 

 freedom from iron oxide, for their large amount of water, and their low specific 

 gravity."' " 



These anomalies are explained by the results of my recasting of his 

 analysis: antigorite, 95.13; deweylite, 4.G3; hyalite, 0.40. In develop- 

 ment of the pseudomorphs, niarmolite from brucite and chrysotile-asbes- 

 tos from nemalite, a steady progression in contraction is shown, to about 

 one-third of the volume, without disturbance by expansion, from the 

 original magnesium hydrate to the final product, antigorite. This seems 

 to be correlated with the perfect preservation of all structural details, 

 even to the most delicate features of nemalite. 



This genetic history of chrysotile, if accepted, enables us to use its 

 occurreiK^e as a test of conditions which have always prevailed during 

 genesis of antigorite from decay. Its general association with the other 

 forms of that mineral, even at the "stubachite" locality, establishes iden- 

 tity of origin through the dual processes already explained. 



Colloid deweylite, the magnesian companion of brucite in migration 

 from laterite, has likewise been concentrated in simple veins, as at Texas, 

 Pennsylvania, Bare Hills, Maryland, etc. Where a portion of the dewey- 

 lite has escaped the subsequent alteration, its intermixture has produced 

 the waxy, translucent variety of antigorite, retinalite, common at many 

 localities. Its analyses invariably reveal an unusually high percentage 

 of combined water, due entirely, as shown by the recasting, to the pres- 

 ence of several per cent, of unaltered deweylite. Moreover, specimens are 

 not uncommonly sprinkled with visible grains of that mineral. 



"Rpt. Prog. Geol. Surv. Can.. 205. Ottawa, 1860. 

 18 Am. Jour. Sci. (2). XXVI, 08. 1804. 



