DIAMOND: SPECIFIC GRAVITY 127 



Since the discovery of the South African diamond-fields, large diamonds have become 

 less rare ; as we shall see later on, stones up to 150 carats in weight have been found there 

 with comparative frequency, while not a few of several hundred carats have been met with. 

 The largest undoubtedly genuine diamond ever discovered, either here or elsewhere, was 

 found at the Cape, in 1893, and weighed 971 f carats ; a more detailed description with a 

 figure (Fig. 51) of this stone will be given later. Probably the lai-gest crystal of diamond 

 to be seen in a public collection is the " Colenso " diamond, presented to the British 

 Museum by Professor John Ruskin ; this is a symmetrically developed octahedron weighing 

 129f carats. 



It has been already stated that the size of diamonds, as of all other precious stones, is 

 estimated from their weight expressed in carats. It will be, however, difficult for the 

 general reader to form a correct mental conception of the size of a given stone from its 

 weight in carats alone ; hence Fig. 32 is designed to show the actual sizes of diamonds 

 weighing 1, 10, 100, 500, and 1000 carats respectively, each having the form of a regular 

 octahedron, which is the form most frequently presented by crystals of diamond. In the 

 special section devoted to the consideration of the larger and more famous diamonds, figures 

 are given representing the actual sizes of these stones, usually in their cut form (Plates X. 

 and XI.), but in a few cases in their rough form. Plate IX. gives the actual sizes of 

 brilliants varying in weight between one and one hundred carats, and Fig. 44 the actual 

 sizes of rosettes, varying between one and fifty carats. 



3. SPECIFIC GRAVITY OF DIAMOND. 



The specific gravity of diamond as determined by various observers varies between 

 3.3 and 3*7. Reliable determinations made on pure stones free from enclosures have, 

 however, in every case yielded values not lower than 3"50 and not much higher than this ; 

 the mean value may, therefore, be placed at 3'52. The following are values obtained in 

 particular instances by careful observers using pure material : 



3'50 — 3"53 (^Dumas). 



3'524 Brazilian diamond (Damour). 



3-520 — 3-524 Colourless and yellow diamond jErom the Cape (von Baumhauer). 



3-517 Brazilian diamond (J. N. Fuchs). 



3-529 " Star of the South " from Brazil {Halphen). 



3-5213 "Florentine" (Sc^iraM/). 



3-50 Diamond from Burrandong, New South Wales {Liversidge). 



3-492 Colourless diamond from Borneo (Grailich). 



The fall of the last value below 3*5, is due to the attachment of a few air bubbles to 

 the stone during the weighing in water. 



The small differences in the specific gravity values given in the above table are probably 

 due to the presence of various impurities. Since coloured diamonds always contain a small 

 amount of impurity, the specific gravity will vary with the colour, as is shown in the table 

 below : 



Other values sometimes given are : colourless diamond 3'519, light yellow and green 



