Some years ago a black diamond from Borneo was placed in the hand of Gallais the lapidary, to be experimented upon at the expense of the French Institute. The chief object of the test was to ascertain the relative degree of hardness in comparison with some of the other varieties of diamond. In this trial the lapidary wore out his steel wheel and a large quantity of ordinary diamond dust without making the least impression on the surface of the black diamond. Although heavily loaded with weights, it lost none of its roughness, and was heated almost to whiteness by the friction of the wheel, which revolved with great velocity. During the period of this extreme velocity it is reported that a shower of sparks was emitted; but how shall we account for this scintillation, when the ordinary transparent diamond does not give forth sparks when struck by steel? The carbonado, which is amorphous and without cleavage, is also extremely hard. The term “adamas,” which the ancients bestowed upon it as denoting an invincible infrangibility, is not quite appropriate; for although it is far superior in hardness to all other known substances, it is in reality very fragile. And in the power to resist the effect of shock it is also inferior to some of the other gems, and especially the sapphire. Therefore several mineralogists have thought that the ancients really applied the term to steel or to some of the varieties of corundum, like the ruby and the sapphire, and not the diamond. It is curious that this property should be ascribed erroneously to the diamond for so many ages, when a trifling experiment would have disclosed the real condition of things. In the days of the poet Lucretius the gem was believed to be able to resist violent blows. ----“adamantina saxa Prima acie constant, ictus contemnere sueta.”