6 DIAMOND FAMILY. dissipates and burns, and combines with nearly the same quantity of oxygen, and forms the same proportion of carbonic acid, as charcoal. Hence it consists principally of carbon. Physical Characters. When rubbed, whether rough or polished, it shews po sitive electricity; whereas quartz, and the other precious stones, if rough, afford negative electricity, but when po lished, positive electricity. It becomes phosphorescent when exposed to the rays of the sun. Many diamonds, however, do not become phosphorescent, although agree ing in colour, form, transparency, kc. with those which readily become luminous. The smaller acquire this pro perty by a much shorter exposure to the light than the larger ones ; sometimes a diamond that is not phos phorescent, by the mere action of the solar rays may be made so, by previously immersing it for some time in melted borax. Vid. Grosser in Journ. de Physique, vol. xx. p. 270. Geognostic Situation. In Golconda, and other districts in Hindostan, the diamond occurs imbedded in an ochry earth, of a yellow or red colour; at the foot of high mountains, which are said to contain quartz. This ochry earth is frequently mixed with quartz, sand, and rolled masses of different kinds, and the whole is sometimes So firmly conglutina- ted ? as to form a pretty solid conglomerate. In the Ilra- zjls,
