bles, probably chiefly quartz. Only the 

 wear of centuries could produce such a 

 result, however, for, as is well known, it 

 is only with its own dust that the Dia- 

 mond can be abraded to any appreciable 

 degree by any of the means now used for 

 cutting it. 



One important property of crystallized 

 Diamond is that of cleavage parallel to 

 the faces of the octahedron. This cleav- 

 age is of much service in preparing the 

 gem for cutting, as by taking advantage 

 of it, broad, flat surfaces can be obtained 

 without grinding. This property also 

 distinguishes Diamond from quartz, for 

 which its crystals as found in sands are 

 sometimes mistaken. Quartz has no 

 cleavage. The fracture of the two 



minerals is the same, however, being con- 

 choidal. 



The massive forms of the Diamond 

 known as bort and carbonado 

 possess little or no cleavage, thus 

 increasing their value as abrasives 

 and for setting in drills, saws, 

 etc. The true bort occurs as rounded 

 forms made up of a confused aggregate 

 of crystals and is harder than ordinary 

 Diamond. Fragments of crystals of no 

 value as gems or any crude Diamond dust 

 are also known as bort in trade. Car- 

 bonado is a name given to black Diamond 

 which has more or less crystalline struc- 

 ture. This graduates into the crystallized 

 mineral. Either of these is more valuable 

 than the crystallized Diamond for indus- 

 trial purposes, although of no value as 

 gems. 



As already noted, Diamond occurs of 

 various colors, about half the stones 

 found being tinged to some degree. If the 

 color is but slight, the stone is considered 

 less valuable than if perfectly colorless, 

 but a Diamond of pronounced color is the 

 most valuable gem known. 



Among colors of Diamonds, blue is the 

 rarest. The largest and most valuable 

 colored Diamond known is the Hope 

 Blue, weighing 44^^ carats. This is val- 

 ued at about one hundred thousand dol- 

 lars. It has a brilliant deep blue color and 

 is without a flaw. A deep blue Diamond 

 weighing 6y 2-16 carats was long worn 

 in the French crown, but it was stolen in 

 1792 and has never been recovered. Red 

 Diamonds vary in hue from ruby red to 

 rose, the latter being the most common. 



No large red Diamonds are known, the 

 largest being one of 32 carats in Vienna. 

 Another famous one is that in the Rus- 

 sian treasury, for which Paul I paid one 

 hundred thousand roubles. It is of a 

 ruby color. The finest green Diamond 

 known is the "Dresden Green" pre- 

 served in the Green Vaults of Saxony. It 

 was purchased by August the Strong in 

 1743 for sixty thousand dollars. It is 

 apple green in color and weighs 40 car- 

 ats. Diamonds of yellow color are com- 

 paratively common, many of the Cape 

 Diamonds being lowered in value by pos- 

 sessing a yellow tinge. It is said that 

 this injurious yellow tinge can be over- 

 come by dipping the stone several times 

 in a solution of potassium permanganate, 

 the violet color of the latter neutralizing 

 the yellow of the Diamond. The yel- 

 low tinge usually also disappears in arti- 

 ficial light. Of large Diamonds possess- 

 ing a yellow color the Florentine and the 

 Tififany are the best known. The color 

 of colored Diamonds is generally perma- 

 nent, but that of some is said to fade on 

 exposure to light. It can also be de- 

 stroyed or changed by heat. 



The luster of the Diamond is a peculiar 

 one, and such as is possessed by few 

 other minerals. In reference to its oc- 

 currence in the Diamond it is known as 

 the adamantine luster. It combines the 

 peculiarity of an oily luster with that of 

 glass and that of a metal. It is doubt- 

 less due to the high refractive power of 

 the mineral, which causes more than the 

 ordinary number of rays of light to come 

 to the eye. In the impure forms of Dia- 

 mond the greasy or oily luster becomes 

 more pronounced. Once the eye becomes, 

 accustomed to the peculiar luster of Dia- 

 mond the stone may easily be distin- 

 guished by it from glass or minerals with 

 a vitreous luster, such as quartz. Certain 

 other minerals, however, such as cerus- 

 site, zircon, and to some extent sphene, 

 exhibit the adamantine luster. In the 

 glass known as strass, used to make im- 

 itation Diamonds, the adamantine luster 

 is well imitated. 



Diamond is usually transparent, but it 

 may be translucent and even opaque, es- 

 pecially the black varieties. Even other- 

 wise transparent Diamond often contains 

 inclusions which cloud and interrupt its 

 clearness. These constitute the "flaws" 



