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PRECIOUS STONES.

effect of hue may be noticed in small parcels of cut emeralds—cut, it may be, from the same stones. And it cannot be doubted that the dichroism of the emerald plays a part in producing its peculiar colour effect. The aquamarine is also dichroic, a sea green specimen showing straw white and grey blue as twin colours.

The range of colour in the beryl is not very extensive; colourless specimens occur, but usually the palest beryls have a faint greenish or bluish tint. The most usual colours are pale green and pale blue with intermediate hues. The true deep rich green of the emerald is rare, but pale yellow, honey yellow, and yellow brown beryls are not uncommon. Sometimes this stone occurs with a rose tint.

The best emeralds occur near Muzo, about ninety-seven miles N.N.W. of Bogotà in the Republic of Colombia, South America. The stones occur in isolated and implanted crystals and in geodes in a calcareous rock in which are very fossiliferous concretions of bituminous character; the emeralds are accompanied by calcspar, gypsum, quartz, pyrites and parisite. The rock belongs to the Neocomian formation. From this locality and from another known as Somondoco and situated about half a degree east of Bogota, it is probable that the fine emeralds secured by the Spaniards in their South American conquests of the 16th century had been originally derived. The really ancient source of emeralds before the discovery of the New World is, however, to be found in Upper Egypt: the mines occur in a depression of the mountainous range which borders the Western coast of the Red Sea. One group of mines is situated on Mount Sakketto, the other on Mount Sabara. The gems are generally full of flaws and poorer in colour than the fine specimens from Colombia.

Fine beryls occur in the Urals at several localities in the neighbourhood of Ekaterinburg, especially near Mursinska. There are other Siberian localities of importance where good aquamarines are found. In this connection must be named the occurrence