64 REVIEWS 



lowing this idea, ruby and sapphire are treated under corundum ; 

 emerald and aquamarine, under beryl, etc. 



At the outset a brief discussion of the nature of gems is given, and 

 the characteristics or qualities for which they are prized are enumerated. 

 Following a few pages devoted to the geographical and geological 

 occurrences of gems, the more common methods of gem-mining are 

 described. Since the coloring of gems is one of the most essential 

 features of their value, the significance and meaning of the color ele- 

 ments are considered, and a list of gems is given arranged according 

 to colors. The subjects of luster and hardness come next, followed by 

 a table showing the hardness of gem minerals. Methods for the 

 determination of specific gravity are described, since herein is a reli- 

 able means of distinguishing between gems of different kinds, and of 

 separating false from real stones. Next comes in turn, a discussion of 

 the optical properties, electrical properties, phosphorescence, and 

 fluorescence of gems. The crystal form of gems is then considered to 

 some extent, since this characteristic often affords a ready method for 

 their identification. Methods of cutting and mounting gems are given 

 in some detail, and a number of line engravings have been prepared 

 showing the usual forms of cutting. Next come chapters on the valu- 

 ation and price of gems, imitation gems, and how to detect them, 

 superstitions regarding gems, and birth-stones. 



Following the general matter noted above, the individual gem 

 minerals are considered, the first being the diamond. In the discus- 

 sion of the diamond its characteristics are pointed out, and the diamond 

 fields and the famous diamonds that have been discovered are described, 

 along with much other matter of general interest. In a similar fashion, 

 the several gems afforded by the mineral species corundum are dis- 

 cussed ; and then come in turn spinel, beryl, chrysoberyl, tourmaline, 

 topaz, garnet, opal, and all other minerals, as well as some substances 

 of animal and vegetable origin which have been used to any degree 

 for purposes of adornment. 



The book is neatly printed and bound, and contains a large num- 

 ber of half-tones and line engravings, as well as sixteen full-page 

 illustrations in color of rare excellence. In bringing together in com- 

 pact form so very much interesting matter concerning our gem miner- 

 als, Dr. Farrington has performed a service that will be greatly 

 appreciated both by the mineralogist and the general reader. 



H. L. 



