About the Chapada Diamond and the Chapada District in Brazil

THE CHAPADA.

Peculiarities of Brazilian Stones--A Diamond-Bearing Rock--A Notable Gem, named after the District where it was found.

In a recent number of the American Journal of Science, Mr. A. O. Derby, in a paper on the geology of the diamond, gives some interesting results of his researches. It has been generally stated that the Brazilian diamond has its matrix in itacolumite, which is a granular quartzose rock sometimes flexible. Mr. Derby, however, shows that, under the name of itacolumite rocks, two distinct geological series have hitherto been confounded. The diamond-bearing rock of Grao Mogul probably belongs to the newer of the two series; but the stones have not been formed in these rocks, and occur there only as derivative bodies like the associated pebbles. At Sao Jao de Chapada the diamond is found in a deposit of clay; and its original matrix is described as a vein of quartz accompanying a rock of unknown nature, but containing iron and crystals of tourmaline, traversing a series of schists and itacolumite. Mr. Derby is of opinion that the original diamond formation in Brazil is probably of Cambrian age. A notable diamond of 87 1/2 carats was found in 1851, in the rich mineral district of Chapada, or Santa-Cruz-da-Chapada, three leagues North-East of Fanado, in the province of Minas-Geraes, Brazil It has been named after the district that produced it.