318 



100.0 



This variety of Serpentine is capable of being decomposed by 

 boiling sulphuric acid, and was at one time used in the manufac- 

 ture of sulphate of magnesia. 



It is too soft to be used for ornamental marble, but it with- 

 stands heat perfectly after it has been gradually baked, so as to 

 expel its water of composition. 



It comes nearer to the precious or noble Serpentine in compo- 

 sition than to that of the Serpentines of Verd Antique Marble, 

 which are much harder than noble Serpentine. 



Dr. Hayes remarked that he was pleased to have his analytical 

 results confirmed, and he considered that no doubt, in relation to 

 the ornamental stone from Roxbury being a mixture of anhy- 

 drous carbonate of magnesia, and a magnesian rock, could longer 

 exist. 



In regard to the presence of any lime in the mixture, the 

 numerous analyses made by himself had not shown a particle, 

 strictly speaking, as belonging to the composition of the rock. 

 Any little cavity showing dolomite crystals or granules is to be 

 considered foreign, as is the case when aggregates of talc crys- 

 tals, or compact asbestos occur. 



The dark portion of the rock, as has before been stated, can- 

 not be considered as a true Serpentine, but as an assemblage of 

 silicates of alumina and iron, with silicate of magnesia. Such a 

 composition as would be given by a mixture of ordinary slate 

 and serpentine. This mixed rock is cemented, as it were, by 

 the anhydrous carbonate of magnesia, which generally exceeds 

 thirty per cent, of the weight of the average of the rock as 

 worked. 



That the name " Verd Antique Marble," as applied to this 

 ornamental stone, is a misnomer, must be apparent to every one ; 



