Diamond is much the hardest substance known in Nature, and as the proverb says only the Diamond is able to “cut Diamond.” It is ranked 10 in the scale of hardness on which minerals are classified, corundum being the next below it. It is really separated by a wide gap from the latter mineral, however, and its hardness is as much greater than that of corundum as that of corundum is greater than that of the first mineral in the scale. This hardness of Diamond affords a ready means of identifying it, as it will scratch all other substances. It is popularly supposed that Diamond is the only mineral which will scratch glass to any extent, and a stone found is often reported to be Diamond because it will do this. As a matter of fact, however, all quartz will scratch glass and the harder minerals, garnet, topaz, beryl and others will do so easily. Minerals which will scratch glass are therefore common. The Diamond cuts glass instead of scratching it, and is the only mineral that will do this. Although the Diamond is so hard, it is not tough, and can be easily broken with the blow of a hammer. It was a tradition of the ancients that if a Diamond were put upon an anvil and struck with a hammer, both hammer and anvil would be shattered without injuring the Diamond in the least. One occasionally hears this statement made even at the present day. It is entirely untrue, however, the Diamond being as brittle as at least the average of crystallized minerals. The specific gravity of the Diamond is about three and one-half times that of water, determinations showing variations between 3.49 and 3.53. Carbonado is lower, ranging between 3.14 and 3.41. Diamond is thus a comparatively heavy mineral, the only ones among the gems which much exceed it in specific weight being hyacinth, garnet, ruby, sapphire and chrysoberyl. Diamond becomes strongly electric on friction so that it will pick up pieces of paper and other light substances. It does not retain its electricity long, however, usually not over half an hour. It is not a conductor of electricity, differing in this respect from graphite, which is a good conductor. Diamond becomes phosphorescent on rubbing with a cloth, giving out a light which is visible in the dark. Some stones emit such a light after being exposed to the sun’s rays for a time, as if they took it up from the sun and gave it out again. This has often been stated to be a property of all Diamond, but this is not true, only certain stones exhibiting it. As first suggested by Mr. Geo. F. Kunz, it is probable that this phosphorescence is due to minute quantities of hydrocarbons which emit light on being heated by the friction given the stone. It is curious to note that the light is in some cases given out only from certain crystal faces of the stone. Thus Diamonds are known which give out light from the cubic faces but not from the octahedral, while others are reported as giving out light of different colors from different faces.