of
the finest specimens known. The place where they were first worked by
Europeans, and whence they had been previously obtained by the
natives, was at Somondoco on the eastern slopes of the Cordillera of
Bogota ; these deposits, though still sometimes worked, do not yield
very fine quality stones. Afterwards another deposit was found on the
western slopes of the Eastern Cordillera to the east of the Rio
Magdalena and near the town of Muzo, lying to the north of the capital,
Bogota. This is now the principal locality in which the gem is found ;
the mineral occurs in a dark bituminous limestone, and the crystals are
usually implanted on Calcite, the latter occurring in cavities in the
limestone (Fig. 21). This deposit is of interest in another way,
because it practically forms the only exception to the rule that
Emerald occurs in granitic and dynamo-meta-morphic rocks. The
associates are exceptional also, Gypsum, Pearlspar, Quartz, Iron
Pyrites, and a rare mineral called Parisite being found with the
Emerald. Many of the specimens show the dislocations, but in this case
the material filling the fissures is Calcite and not Quartz. The
stones, too, are prone to become turbid after a time from the formation
of numerous minute flaws. Emeralds of gem quality are known locally as
Canutillos, and those not fit for cutting as Morallons.
Also
in South America, in Brazil, Beryl occurs in some quantity in the
north-east of Minas Geraes, associated with Topaz and Chrysoberyl ; the
crystals are often of several pounds weight, but the larger ones are
usually, as elsewhere, cloudy and in a large part unfit to cut. The
mineral here is probably derived from a granitic rock. Near Bio de
Janeiro, too, Beryl occurs in pegmatite bands
