ORIGIN DiAmoNns. The problem as to the origin of the diamond, once a favorite subject of speculation, has been studied recently by scien tists with some success. In this connection. the South African fields are most significant. As previously stated, the deposit: are circular or oval in form, and it has been found that they arc' inclosed by a wall of carbonaceous shale. For a considerable distance below the surface, the deposits consist of a yellowish, friable mate rial called by the miners 'yellow ground.' but when, with depth. the limit of atmospheric weathering has been reached, they pass into a partially serpentinized olivine-pyroxene rock of igneous character, known as 'blue ground.' Ilese facts indicate that deposits occupy the vents or pipes of ancient volcanoes, and it is there fore probable that the presence of the diamond connected with volcanic activity, the stones either having been brought up from the interior of the earth, or having been formed in place under the influence of the molten rod: in con tact with the carbonaceous shale. The French geologist De Launay has argued that the dia monds have come up from below. This view scents to be supported by the fact that their occurrence is apparently independent of the en closing rock, whether this be the carbonaceous shale found at the surface or the underlying dia base and quartzite. The conditions necessary for the crystallization of carbon in the form of diamond would seem to be intense heat and great pressure. such as exist during the forma
tion of igneous rocks. Sueeessful attempts to reproduce these conditions artificially have been carried out by Professor Alois:an of Paris• and also by the English chemist l'rofes:or Crooke:. The method Ciliplo•Pd consists in heating pure prepared carbon and iron in an electric furnace. By sudden cooling of the molten the surface contrails and exerts a powerful pressure upon the interior mass. When cold. the iron is dis solved in acid. and small black particles remain which exhibit the properties of genuine dia monds.
V vi IT. The value of gem IllanlOnd: cannot be determined by absolute standards. NVeight. cut, brilliancy. color, and perfection of the stones are factor: that nmst be considered in estimating the cable. Which is, moreover, subject to Ibletua tion. Colorless 'tones bring hi•her prices than off eolored stones, but if decided tints of red. blue, or L•1'1,11 are present they may increase the value abnormally. The value ordinarily in creases in a ratio increasing with the weight. but this rule does not hold good for the largest stones, the prices of which cannot be fixed. Dia monds in the rough generality average $S to $15 the carat for the run of the mine.