Precious Stones. 219 



tlie solid crystalline state in which the diamond is found. 

 Liquids, such as ether, alcohol, etc., show us this same sub- 

 stance (in combination) in another physical condition ; but we 

 do not know how to make a solution of carbon in any fluid 

 that will deposit it on evaporation in a crystalline pattern, nor 

 can we fuse carbon like sulphur, and obtain our crystals as it 

 cools. Carbon is pre-eminently a vegetable material, and plants 

 as they grow collect it from the air, and assimilate it in their 

 tissues. United with oxygen and lime, or magnesia, carbon 

 also abounds in terrestrial rocks; but it is remarkable that 

 animals low in the scale of organization, like the coral polyp 

 or the rhizopod, are the great agents in building up strata 

 of this kind. How nature deals with carbon in the production 

 of the diamond is imperfectly guessed, not known. This work 

 may be slow, so that ages may elapse before one of the 

 precious crystals may be completed, or it may, under appro- 

 priate circumstances, be rapid, though apparently seldom per- 

 formed. It may be due entirely to chemical and electrical 

 agencies, or, as many suppose, the organic life of the plant 

 may in some way be concerned in the formation of the gem. 

 However it is produced, it is the hardest substance known. 

 Mr. Emanuel says "it is found both in regular crystalline 

 forms and in an amorphous state. The crystals are principally 

 octohedrons or dodecahedrons, the planes of which have fre- 

 quently the peculiarity of being either concave or convex; 

 sometimes they are worn, by attrition or other causes, into 

 heterogeneous forms, being nearly round balls, occasionally 

 transparent, or covered with a thick crust." Its specific 

 gravity is about three and a half times that of water, and 

 its beauty is due to its optical properties. It refracts light 

 very powerfully, reflects it from its inner surfaces very per- 

 fectly, and disperses or spreads the ray so as to exhibit the 

 rainbow colours in a very splendid way. Mr. Emanuel gives 

 the following comparison between the diamond and glass : — 



THE DIAMOND. 



Eefraction 2 -48 7 



Dispersion 0"38 



GLASS. 



Eefraction l - 525 



Dispersion 0*32 



From these properties arises the beautiful effect of a diamond 

 receiving light from one direction, and pouring forth its coloured 

 rays in another direction, where the radiance may look all the 

 brighter through contrast with surrounding shade. 



If diamonds were large, cheap, and perfectly homogeneous, 



