274 F. D. Adams — Melilite bearing Rock. 



When thin sections are treated with cold diluted hydrochlo- 

 ric acid the magnesite remains unaltered, even cold concentrated 

 hydrochloric acid does not dissolve it. When however the acid 

 is warmed the greater number of the magnesite pseudomorphs 

 are completely dissolved, others however, are only partially dis- 

 solved, or are dissolved only in certain places, owing apparently 

 to the fact that in these cases the alteration into magnesite is not 

 yet complete or is complete only in certain parts of the pseudo- 

 morph. By carefully searching a large number of hand speci- 

 mens it was found to be possible to obtain a sufficient amount 

 of the magnesite apparently quite pure, to enable its blowpipe 

 characters to be determined and also for chemical analysis. 

 Before the blowpipe it decrepitates somewhat and blackens but 

 does not fuse even on the thin edges. After ignition it shows 

 an alkaline reaction with turmeric paper and in its other blow- 

 pipe reactions, which it is unnecessary here to detail, agrees with 

 magnesite. A small fragment placed in cold concentrated 

 hydrochloric acid gives off a few minute bubbles but goes into 

 solution only with extreme slowness. The specific gravity of 

 four little fragments was taken by the aid of Thoulet's solution 

 and a Westphal's balance and was found to range from 3'062 

 to 3-072 at 19-5° C. 



The following analysis of the apparently pure material re- 

 ferred to above, dried in vacuo over sulphuric acid, was kindly 

 made for me by Dr. B. J. Harrington. 



MgO 32-68 



CaO_. 0-93 



FeO 16-24 



C0 2 , 44-61 



Si0 2 3-38 



HO 2-13 



99-97 



When the combinations are calculated the percentages of the 

 carbonates are found to be as follows : 



MgC0 o 64-83 



FeC0 3 ° 26-16 



CaC0 3 ... 1-66 



This leaves an excess of- 181 p. c. of magnesia, which is 

 probably present as a hydrous silicate. The silica, which 

 remains behind in a flocculent condition when the mineral is 

 treated with hot hydrochloric acid, is probably derived in part 

 from a little serpentine present as an impurity. 



