222 ANNUAL. REPORT SMITHSONIAN INSTITUTION, 1911. 



Table III. — Composition of the principal precious stones. 



Element. 



Oxides. 



Aluminates. 



Silicates. 



Species. 



Diamond. 



[Corundum 



Quartz. 



Spinel 



Chrysoberyl. 



Beryl 



Variety. 



Garnet. 



Olivene 



Sphene 



Spodumene. . 



Topaz 



Tourmaline. . 



Zircon. 



Turquoise. 



Opal 



Pearl 



[Ruby 



■j Sapphire 



lOriental amethyst, etc . 



I Crystal 

 Amethyst 

 Cairngorm, etc 



Balasruby, etc 



|Cymophane 



[Alexandrite 



(Emerald 



I Aquamarine 



IHessonite 

 Pyrope 

 Almandine 

 Demantoid, etc 



(Peridot) 



(Kunzite). 



[.Targoon... 

 {Hyacinth . 



Composition. 



Carbon. 



Oxide of aluminium. 



Silica. 



Magnesium aluminate. 

 Beryllium aluminate. 



Beryllium aluminium silicate. 



Calcium aluminium silicate. 

 Magnesium aluminium silicate. 

 Iron aluminium silicate. 

 Calcium iron silicate. 

 Magnesium iron silicate. 

 Calcium titanium silicate. 

 Lithium aluminium silicate. 

 Alu min ium fluo-silicate. 

 Complex alkali-lime-alumina silicate. 



Zirconium silicate. 



Hydrous aluminium phosphate. 

 Hydrous silica. 

 Calcium carbonate. 



The most important point to remember about paste, however, is 

 its lack of durability; it is not only too soft to stand much wear, but its 

 composition is so unstable that it rapidly deteriorates and loses its 

 brilliancy on exposure. You will see, therefore, that although there 

 is a certain legitimate scope for such paste imitations they are very 

 unsatisfactory substitutes for the genuine article. This being the 

 case, as scientific knowledge has advanced, attention has been more 

 and more concentrated on the problem of producing by artificial 

 means the actual minerals found in nature, and thus obtaining what 

 I have defined as artificial in contradistinction to imitation jewels, 

 having both the beauty and durability of the natural article without 

 the objectional concomitant of enormous cost. 



The first point to be considered in attacking this problem is the 

 composition of the stone, as it is obvious that, other things being 

 equal, the possibilities of success are greater with one of simple than 

 one of comparatively complicated composition. One also has to 

 consider, however, the economic aspect — it is not much use devoting 

 time and ingenuity to the production of an artificial stone when the 

 natural one is so common that the cost of the two would be practically 

 identical. 



