In the Cavities of Minerals. 31 



every mineralogist who saw them considered them as something 

 new in appearance, I expected that a greater quantity of them 

 might be found for the purposes of analysis. Familiarised, there- 

 fore, with the aspect of these groups, I was convinced that the 

 crystals in the fluid cavity were the same substance ; and a more 

 accurate examination has established their perfect identity. 



These white crystals sometimes occur in minute insulated 

 spiculae within the solid mass, but most frequently in spherical 

 groups of extreme beauty, surrounded with the most transparent 

 quartz. Many of the open hollows and crevices of the quartz 

 crystals are filled with them, and numerous aggregated groups 

 adhere to their external surface. These crystals, though very 

 minute, I have found to have a powerful double refraction ; 

 and as they are wholly dissolved with effervescence, excepting a 

 little adhering silex, in diluted nitric acid, there can be no doubt 

 that the external crystals and consequently those in the fluid ca- 

 vity, are carbonate of lime *. 



SECT. VIII. On the Phenomena of a single Fluid in the Cavities 

 of Minerals and Artificial Crystals. 



The phenomena which I propose now to describe, are essen- 

 tially different from those which form the subject of the preced- 

 ing sections. The fluid which occupies this class of cavities ex- 

 hibits no properties different from water or mineral oil, which 

 have long ago been detected by mineralogists, and the vacuity 

 which often accompanies these fluids, is either a perfect vacuum, 

 or filled with a gaseous body. 



* Since these observations were made, Mr NOUDENSKJOU> has confirmed this 

 result by experiments made with the blowpipe. 



