MINERALOGY. 69 



I. II. 



Silica, 68.84 68.35 



Alumina, 16.47 17.60 



Glucina, 1340 14.00 



Iron oxide, 1.70 trace. 



Chromium oxide, ...... trace. 



100.41 99-95 



The analysis by Prof. Joy is the result of an extended series of experi- 

 ments which were made with the view of finding the best methods to 

 analyze this species, and to obtain glucina in a state of purity in order 

 to study its properties and its salts. 



The fracture of beryl is vitreous. It sometimes shows a basal cleav- 

 age, and this cleavage is very marked and perfect on the very large 

 specimens. 



A thin section of one of the large beryls from Grafton shows that the 

 crystal is filled with microscopic impurities. Its appearance under the 

 microscope is represented in Fig. 4 on PI. 4. There are amorphous sub- 

 stances that have filtered into the cracks ; and there are crystalline sub- 

 stances. These latter are all prismatic, and are arranged with an edge of 

 the prism parallel to the long axis of the beryl. The minerals are those 

 that are common in the granite veins. There are little black tourma- 

 lines, and scales of black mica. Beside these there are minute particles 

 that polarize the light like quartz, and numerous cavities that are filled 

 with water, each one containing a bubble of air. These cavities are 

 generally wholly irregular, but others have a perfect hexagonal outline, 

 with the long axis and the sides parallel to those of the large crystal. 

 Like the other cavities, they contain a fluid and a bubble. Most of these 

 cavities probably contain water ; but one that I examined apparently 

 contained two fluids, and the bubble disappeared at a temperature of 30° 

 centigrade. It therefore contained liquid carbonic acid, which has been 

 shown by Sorby and others to be common in beryls. 



The expansive force of liquid carbonic acid at 0°, C. is '^6 atmosjDheres, 

 and increases one atmosphere for every added degree of temperature. 

 If, as is likely, the temperature was an elevated one under which these 

 minerals were formed, the pressure must have been immense. 



