Q% nSaVtAR CliYSTALLIZATTON OP THE DIAMOND. 



has been tuianimously confirtired by comparing it with ano- 

 ther fraf^ment, in which likewise are found a number of grains 

 of lazulite, enchased as it were in carbonate of lime, equally 

 accompanied with sulphuret of iron, all of the same azure 

 blue colour, and some of which pretty distinctly exhibit 

 angles and faces, notwithstanding their smallness. 

 Sonaehtveun- Most of the mineralogists who have written since this 

 reasonably P^^^'^^^t'on have made no scruple to mention this regular 

 figure under the article lazulite ; though others have not 

 even attempted to fix their opinion by an examination of 

 the crystal, a description of which I have published. They 

 have concluded, that, being opake and mixed with pyrites 

 and carbonate of lime, there was no proof of its being 

 really a lazulite; notwitl-rstanding they agree with all other 

 mineralogists, that the fossile body which yields ultramarine 

 is always opake, and commonly mixed with pyrites and car- 

 bonate of lime. 

 New cystal of Having had an opportunity of observing a crystalline form 

 of the diamond perhaps hitherto unique, 1 conceived the 

 Class would receive some gratification from seeing it, and 

 that this would be the most certain method of establishing 

 W existence beyond all controversy. 

 Usual form of The primitive form of the diamond is known to be a re- 

 us crjsta s. guiar octaedron. Most frequently it presents itself in sphe^ 

 roidal crystals or with curvilinear facets. It has been found 

 cubical, plano-convex, cyliudroid : but it was not suspected 

 to be susceptible of that variety of form, which Rome d<* 

 ITsle termed made, and Mr. Haiiy has named liemitrope ; 

 that is, where half of the crystal is turned back, so as to 

 form reentering angles, as we see in some varieties of the 

 ruby, feldspar, pyroxene, Jcc, 

 AmacUor Among the rough diamonds, which Mr. d'Arcet offered 



twmcrystel. ^^ sacrifice to the series of experiments undertaken by 

 Messrs. Hachette, Clement, and myself, on the products of 

 their combustion, there was one, which we thought proper 

 to set aside, as presenting the first example of a structure, 

 the prototype of which ought to be preserved. 



This diamond is of the weight of 702 millig. [11 grSr 

 nearly]. Its specific gravity is J*512. 

 The class will perceive at once, that it is formed of two 



demispheroids. 



