548 ANALYSES OF SERPENTINE. 



" The results to which I have arrived possess some scientific as well as practical interest, 

 for they show a curious replacement of carbonate of magnesia for carbonate of lime, the 

 rnagnesite being most abundant in the Vermont marble [serpentine], while calcite is the 

 predominant spar in the European variety. 



" Serpentine consists essentially of hydrous silicate of magnesia and silicate of the 

 protoxyd of iron, with occasionally a little oxyd of chromium these oxyds giving the 

 green color to the serpentine. The presence of water in composision in serpentine mate- 

 rially affects its hardness, the softer varieties containing the largest proportion of water. 

 In some varieties I found as much as fifteen per cent., while the lowest was seven per cent. 

 Both the verd-antique serpentine of Europe and of Roxbury, Vermont, contain between 

 twelve and thirteen per cent, of water. That from Proctorsvillc, Vt., contains but seven 

 per cent., and that of Roxbury thirteen, while that from Europe contains 12.5 per cent. 



" Verd-antique marble may be defined to be serpentine mixed with, or containing numer- 

 ous veins of magnesian carbonate of lime. The relative proportions of these ingredients 

 may vary considerably on account of the isomorphic or rather plesimorphic characters of 

 the two minerals. Carbonate of the protoxyd of iron, in like manner being plesimorphic 

 with both carbonates of lime and of magnesia, replaces either of those minerals in all 

 proportions, without changing the angles of the crystals more than one degree. 



"It will be observed on examination of the analyses I have made, that in the Vermont 

 serpentine the white spar veins are chiefly composed of magnesite, while there are also 

 veins consisting of magnesian carbonate of lime, and of carbonate of iron. The relative 

 proportions of these magnesian and ferreous carbonates, in the Vermont marble, are nearly 

 the reverse of those in the European variety ; thus beautifully illustrating the law of 

 isomorphous substitution of mineral ingredients. 



" I. Chemical analysis of the white veins of European Verd-antique. These veins, 

 picked out with great care, to avoid any mixture of particles of serpentine, yielded per 

 cent, 



Carbonate of lime, .... 81.00 

 Carbonate of magnesia, . . . . 13 .70 

 Carbonate of iron, . . . . 7.30 



100.00 



" II. Chemical analysis of the white veins of Roxbury Vt., Verd-antique marble. These 

 veins were quite common in the slab examined by me. They were picked out with care 

 to avoid any admixture of serpentine. On analysis, they yielded, 



Carbonate of magnesia, . . . 80.00 



Carbonate of lime, .... 15.00 



Carbonate of ii*on, .... 3.50 



Silica, and loss, 1.50 



100.00 



" It will be observed that the carbonate of lime in the European marble is represented 

 by carbonate of magnesia in the Vermont variety, and the carbonate of magnesia by the 

 carbonate of lime a reversal of these ingredients. 



