CONTENTS 



CHAPTER XII 



GEMS, NATURAL AND ARTIFICIAL 



Ancient and modern superstitions about gems, p. 295 Confused 

 nomenclature, p. 297 Practical tests, p. 300 Mohs' scale of hard- 

 ness for gems, p. 301 Methods of testing, p. 302 Tables giving 

 specific gravity of gems, p. 303 The dichroscope, p. 304 The 

 cutting of precious stones, p. 305 Bruting, polishing, and clean- 

 ing, p. 306 How gems are cut, p. 307 Various forms of diamond- 

 cutting, p. 310 Cleaving precious stones, p. 310 Strength and 

 skill in diamond-cutting, p. 311 Diamonds in the rough, p. 312 

 Various diamond-bearing earths, p. 313 How diamonds were 

 discovered in South Africa, p. 314 Use of diamonds for mechanical 

 purposes, p. 318 The ruby and its allies, p. 319 Montana sap- 

 phires, p. 321 "Spanish emeralds," p. 324 Artificial gems, p. 

 327 Laboratory-made diamonds, p. 328 How other artificial 

 gems are made, p. 330. 



[vii] 



