| The occurrence of the diamond in alluvial deposits and clays, accompanied by quartz, topaz, tourmaline, rutile, zircon, garnet, etc., throws no light upon the origin of this precious stone, since the crystals are loose and have evidently been borne away by natural agency from their place of origin. Small diamonds have, however, been found embedded in crystals of xanthophyllite, a siliceous mineral, in such a manner as to suggest that they originated there. Moreover, the diamonds in different "pipes" of blue ground in South Africa differ in quality; and this suggests that they may have been formed in the pipes, perhaps by volcanic agency. Diamonds have also been found in meteoric stones, and in meteoric iron accompanied by carbonado and graphite. It therefore seems probable that diamonds have crystallised under suitable conditions from a solution of carbon in a siliceous or metallic solvent. The discovery of diamond, accompanied by carbonado and graphite, in a meteorite found in the Diablo Canon, and its study by Moissan, have thrown much light on the problem and enabled this chemist to prepare small diamonds artificially. |