Mr. T. S. Hunt's Examinations of some Felspathic Rocks. 357 



levigated mineral with five or six parts of carbonate of lime and 

 three-fourths its weight of sal-ammoniac. The agglutinated mass 

 slakes by the action of water, and yields to that liquid its alka- 

 lies in the form of chlorides, with a mixture of chloride of cal- 

 cium. A second ignition of the undissoved residue with two- 

 thirds the first amount of sal-ammoniac ensures the separation 

 of the last portions of alkali. These processes were adopted in 

 all the analyses here given, with some exceptions to be noticed 

 in their places. 



100-15 99-45 99-82 



In another specimen the amount of lime was found to equal 

 7 - 89 per cent. The composition of this felspar is very nearly 

 that of andesine, which,' according to Abich, yields silica, 59*60; 

 alumina, 24*18; peroxide of iron, 1-58; lime, 5*77; magnesia, 

 1-08; potash, 1-08; soda, 6-53 = 99-82. 



The greenish base of the rock is generally finely granular and 

 strongly coherent • the grains possess the cleavage, lustre, and 

 hardness of felspar ; the density of carefully chosen fragments 

 was from 2*665 to 2*668. The greenish-white of the powder is 

 changed to a fawn colour by ignition. When pulverized and 

 digested with acetic acid, the mineral loses two or three thou- 

 sandths of carbonate of lime, with traces of magnesia, iron oxide, 

 and alumina. A portion which had been thus treated and care- 

 fully dried gave the following results : — 



IV. 

 Silica 58*50 



Alumina . . 



Peroxide of iron 



Lime .... 



Magnesia 



Potash 



Soda .... 



Loss by ignition 



100*57 

 It is therefore a felspar differing but little from the crystalline 

 andesine in composition. 



25*80 

 1*00 

 806 



•20 

 1-16 

 5*45 



•40 



