belief
that this sandstone is derived from the weathering of the older
itacolumite, and that it is identical with the sandstone seen lying
unconformably on the itacolumite in the Serra do Espinhaço. Diamonds
were first discovered at Grâo Mogol in the "gurgulho " in 1827, but
were not found in the sandstone till 1833.
The
state of Bahia, which was formerly of small importance as a Diamond
producing region, has latterly been more productive than Minas Geraes.
Diamonds were discovered in this state in 1755.
Near
Salobro, on the Rio Pardo, nearly 200 miles south-south-west of the
town of Bahia, Diamond occurs in clays, in crystals of good quality,
octahedral in type. They are supposed to be derived from the
crystalline rocks around, but the absence of certain minerals
characteristic of these rocks in Brazil has led to doubt being thrown
on this origin. Further, although the general mineral associates are
much the same as elsewhere in Brazil, there are some remarkable
exceptions in the presence here of Corundum and the absence of
Tourmaline and the oxides of titanium.
West
of Bahia about 200 miles, in the Serra da Cincora, a rich deposit was
discovered in 1844, and since that time a large quantity of stones has
been obtained from the locality. The Diamond here occurs in alluvial
and other detrital deposits, although the hills around are of granite
and gneiss.
Most of the Carbonado produced comes from this locality.
In
Borneo deposits have been known for a long time, but have never been of
any great importance in comparison with the foregoing great areas of
production. One group, in the south of the island near Bandjermassim,
is in gravels
