gems, lapis lazuli, Afghanistan, cause of color

Chemists have long made that blue stone, known under the name of lapis lazuli, an object of their research, with a view, in particular, to discover the colouring substance which gives it so high a value; on account of the splendour it communicates to works in which it is employed, and of the ultramarine, so much esteemed in painting, which is prepared from it. This colour was first ascribed to copper; but the celebrated Margraf demonstrated the fallacy of this opinion, as he found in it only silex, sulphat of lime, lime, and a little iron. Some after him suspected in it the presence of the oxyd of cobalt; and others, such as Rinmann, a little fluoric acid: but all these conjectures, by a more accurate examination, were soon shown to be false.