CATALOGUE OF GEMS. 501 



mens. Practically all of the l)luc .stoiios known have ])eeii i'oinul in 

 India, and their occurrence i.s as rare as the red. (Unnanion, brown, 

 V)lack, milky, and opalescent stones are occasionally met with. Pure 

 colorless diamonds without a flaw or tint of any kind are more lare 

 than is generally supposed. 



The specific gravity of the diamond is 3.52; hardness, 10; crystalli- 

 zation, isometric; cleavage, octahedral and perfect; refraction simple, 

 with an index of 2.J:3*J; a high dispersive power; luster, brilliant 

 adamantine; is combustible though infusible; positively electric ]\y 

 friction; a nonconductor of electricit}^; is phosphorescent; does not 

 polarize light, and consists essentially of carbon. 



Three forms of the diamond are recognized: First, crystallized, the 

 one employed in jewelry; second, crystalline, or imperfectl}^ crystal- 

 lized, having a hardness greater than that of the crystals and known 

 as bort; this term is applied also to chips, diamond waste, and stones 

 unsuited for cutting; third, an impure kind called carbonado; this is 

 an opaque, steel gray to black, amorphous variet}-, without cleavage. 



Diamonds and all other gems are rated hy the carat. The term carat 

 is derived from the name of certain small leguminous seeds which, 

 when dry, are quite constant in weight. The lirilliant, glossy, scarlet 

 and black seed of Ahrus pecatorlus weighs about 2 grains, and was 

 early used in India for weighing gems. An English carat is e((ual to 

 3.1683+ grains, commonly reckoned as 3.17 grains troy, hence there 

 are 151i carats in an P^nglish troy ounce. Reckoning the value in the 

 metric system, the weight of a standard carat will ])e 0.205 grams. 

 The carat is subdivided into halves, quarters, eighths, sixteenths, 

 thirty-seconds, and sixty-fourths. A quarter carat is called a grain. 

 This is a ''diamond" grain, not a troy grain, and is but 0.7925 of a 

 true grain. In diamonds, perfectly white stones or decided tints of 

 red, rose, greea, or blue are most highly prized. Fine cinnamon, sal- 

 mon, l)rown, black, or yellow stones are also much esteemed. When 

 flawdess and without tint of any kind, they are termed ''first water." 

 If they possess a steely-blue color they are called " blue white." It is 

 impossible to estimate the value of a diamond by its weight. Color, 

 brilliancy, cut, and general perfection of the stone are all to })e con- 

 sidered. Of two stones, both flawless and weighing 10 carats, one may 

 be worth |6o0 and the other 112,000. Ofl'-colored or defective stones 

 may sell at $-10 to $75 a carat regardless of size, while the value of an 

 ordinary good water stone increases in an increasing ratio with its 

 weight up to about 20 carats, beyond which no rule holds good. 

 Exceptionally perfect stones have no fixed value, the price dei)ending 

 upon the purity and brilliance of the stone. 



Some diamonds are celebrated for their size, others for the interest- 

 ing legends connected Avith them. Among the more interesting of 

 these celebrated diamonds are the "Regent" or "Pitt" diamond, 



