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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