458 



Sir David Brewster on the Structure 



This discovery of a new matrix of the diamond takes away the foundations 

 of the argument from which I concluded " that the compressible state of the 

 diamond could not arise from heat/' for it is possible that the rocky matrix in 

 which it was found had an igneous origin ; and Captain Franklin's supposi- 

 tion that it might be fused under compression, is quite conceivable. 



But, though I admit the possibility of the diamond having been in a state 

 of igneous fusion, I consider it highly improbable that it was so. In the la- 

 borious examination, which I carried on for several years, of the cavities in 

 topaz, quartz, amethyst, chrysoberyl, &c., and in salts formed from aqueous 

 solutions, I had occasion to observe the condition of many thousands of cavi- 

 ties, and in no one case, neither in crystals which exist in rocks known to 

 be of igneous origin, nor in crystals artificially formed, have I been able to 

 discover a single cavity in which the expansible fluid which it contained had 

 compressed the surrounding mass, and communicated to it the polarizing 

 structure existing around the cavities in the diamond. 



Now, in glass which is known to have been in a soft state, and in amber, 

 which is generally allowed to be an indurated gum, I have discovered cavities 

 similar to those in the diamond, and surrounded by the same polarizing struc- 

 ture ; a structure which could only be produced by a compressing force 

 emanating from these cavities. 



As I am desirous that mineralogists should thoroughly understand the na- 

 ture of this structure, I have made two drawings of the diamond Laske which 

 contains the cavities under consideration. 



Fig. 1. represents the diamond considerably magnified. At a and h are 

 seen two minute cavities, which appear perfectly black, as if they were filled 

 with opake matter. This blackness, however, arises from the high refraction 

 which takes place at the concave surfaces of the cavity, as may be proved by 

 the apphcation of a microscope, which exhibits a minute pencil of light 

 transmitted through them. Fig;. 2. shows the four luminous sectors around 



