1869.] Rubies, Sapphires, Diamonds, and some other Minerals. 301 



present when the crystals were formed, but penetrated into the fluid- cavities 

 at a subsequent period, and either filled vacant spaces, or removed and re- 

 placed the material of glass cavities, as suggested by Vogekang # . In the 

 specimens which we have examined, each of the cavities contains what is 

 no doubt an aqueous saline solution, and, as shown by fig. 8, one or more 

 cubic crystals, probably chloride of potassium, which dissolve on the appli- 

 cation of heat, and are deposited again on cooling. These cavities are thus 

 analogous to those met with in the quartz of some granite, and in the mi- 

 nerals of blocks ejected from Vesuvius ; and it seems difficult, if not impos- 

 sible, to explain them except by supposing that a strong saline solution 

 was caught up by the mineral at the time of its formation. In some cases 

 the amount of such saline matter is so great in comparison to the liquid, 

 that a high temperature would be requisite to make it all dissolve. It 

 also seems probable that, if water could penetrate into such crystals, it would 

 soon be lost when they were kept dry. This certainly occurs in some 

 soluble salts, especially those containing combined water, and in some 

 minerals of loose texture ; but we have never seen evidence of it when 

 fluid-cavities are completely inclosed in hard and dense substances like 

 quartz or emerald. Though in some instances the size of the bubbles does 

 not bear a uniform relation to that of the cavities, yet in many cases the 

 general proportion is very similar in each specimen ; and the exceptions can 

 easily be explained by supposing that occasionally small bubbles of gas 

 were caught up along with the water, or that there was some variation in 

 either temperature or pressure during the growth of the crystal; all of 

 which conditions were discussed in Mr. Sorby's paper already referred to. 



"We have not had the opportunity of studying many examples of cavities 

 which contain two fluids, probably water and liquid carbonic acid, and 

 therefore forbear to say much about them. According to Brewster f the 

 temperature at which those in topaz become full corresponds very closely 

 with what we have observed in the case of sapphire, so that the carbonic 

 acid might have been inclosed either as a highly dilated liquid, or as a 

 highly compressed gas; but since the other liquid has deposited crystals 

 which dissolve on the application of heat J, it seems most probable that the 

 water was caught up in a liquid state, sometimes perhaps holding a con- 

 siderable amount of carbonic acid in solution as a gas. 



On the whole, therefore, the various facts described in this paper seem to 

 show that ruby, sapphire, spinel, and emerald were formed at a moderately 

 high temperature, under so great a pressure that water might be present in 

 a liquid state. The whole structure of diamond is so peculiar that it can 

 scarcely be looked upon as positive evidence of a high temperature, though 

 not at all opposed to that supposition. The absence of fluid-cavities con- 

 taining water or a saline solution does not by any means prove that water 



* Philosophic der Geologie mid mikroskopische Gesteinsstudien, (Bonn, 1867)pp.l55, 

 196. 



t Trans. Eoy. Soc. Edin. vol. x. p. 1 et seq, 



i See Brewster's paper, Phil. Mag. 1847, vol. xxxi. p. 497* 



z 2 



