34 ANNALS NEW YORK AC Am-] MY OF SCIENCES 



laterite into fissures and occupied them as vein deposits. Magnesium 

 hydrate, the most soluble and mobile, was the earliest to fomi a coating 

 on each wall, sometimes filling up the entire fissure. So originated the 

 veinlets of brucite, crystalline at Iloboken, New Jersey, and crystallized 

 at Hopansuo, Finland, and Texas, Pennsylvania. 



The next stage in the process has been connected with the tendency of 

 brucite, wIkmi subjected to rock-strains, to molecular rearrangement in 

 direction of the pressure. Its grains become shot through with parallel 

 lines, without regard to the cleavage, and at last transformed into aggre- 

 gates of fine fibers. Thus brucite has frequently passed into its fibrous 

 allomorph, iicmalite, with fibration nonnal to the vein walls, well shown 

 at Hobokon and Montville, New Jersey, Xettes in the Vosges, etc. From 

 solution in carbonated waters, veins of the less soluble carbonates, hydro- 

 magnesite, magnesite, etc., have been also produced, or from the action 

 of such waters on brucite already depasited, as at Hoboken, many localities 

 in California, etc.; or whore nemalite has occurred, coating each wall of 

 a vein, the interspace remains sometimes filled up with laminated brucite, 

 as at Hoboken, or with magnesite, as at Montville. 



Next, by ])assage of siliceous waters, crystalline brucite has been con- 

 verted into its antigorite-pseudomorph, marmolite (as shown by Volger 

 and others) at Hoboken and elsewhere, and its crystals into "thermophyl- 

 lite" at Hopansuo. In the marmolite of Hoboken, pearly fiakes of un- 

 tdtered brucite can be sometimes plainly distinguished. This again im- 

 plies the intervention of deweylite, and there is abundant evidence of its 

 generation by the following process — reaction of free magnesium oxide, 

 hydrate or carbonate, or of dolomite, with percolating solutions of silicic 

 hydrate or of alkaline silicates. Of the resulting equations it will suffice 

 here to ofl'er the following : 



4 H,MgO,-h3 (H,Si03-f n aq.) = iH,,Mg,Si30,6 + n aq.) + H,0 



Maeiieniiuii Silicic hydrate Colloid deweylite 



hydrate 



Volume change (disregarding /; aq. ) = — .'5.7.5 per cent. 



Deweylite of this origin, subjected to thermal conditions, passed into 

 antigorite by the reaction already explained. 



Where silicification of nemalite took place, it was converted into dewey- 

 lite with pseudonioi pilous fibration, and this, by later thermal action, 

 into its antigorite-pseudormorph. chrysotile. The passage of nemalite 

 into chrysotile, supposedly direct, was detected by G. H. 0. Volger"' in 

 specimens from Hoboken in his cabinet, but the intervention of deweylite 

 was not suspected. 



i« Entwlckluuir dcr MiiuMalien der Talk-Glimmer Familie. Ziirich, 254-270. 1855. 



