DIAMOND MINES OF BRAZIL 195
usually
found in any locality where " estrellada" occurs. Between its various
colors are white points containing fragments of quartz. These give it
the starry effect for which it is named. It consists of decomposed
stratified rocks reduced to a clay. Among its components are, hornfels,
fragments of opal, and pebbles of augite-por-phyry. The diamonds found
in it are usually small and have an appearance like bort, but cut to
very brilliant stones.
Taua
is similar to estrellada, but is composed of larger fragments and the
white spots are absent. Between alternate plates of red or green
amphibolites and decomposed gray and yellow mica-schist, are pebbles
of augite-porphyry and fragments of opaline chalcedony. In the red or
yellow containing iron oxide and fragments of quartz, which fills the
spaces between the pebbles, the diamonds are found. Taua is the chief
diamondiferous deposit of the Agua Suja district inasmuch as it is
usually greater in depth and carries more diamonds, though the gorgulho
yields larger stones. Being above water level it can be worked more
economically also.
On
both sides of the Bagagem river are shallow beds of gravel consisting
largely of fragments of amphibolites, quartz and hyalo-tourmalines
called " grupiaras." These are diamondiferous but have been about
exhausted. The river beds are undoubtedly diamondiferous but their
value cannot be fully determined without machinery capable of dredging
the bottoms. The deep pools and depressions into which probably the
richest washings of the torrents have been carried, are beyond the
reach of the methods and appliances at present in vogue throughout the
Brazilian fields. For more than a century the
