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Pliny notices (xxxvii. 22) that many were of opinion that this stone was of the same or a similar nature with the Emerald. This opinion has been proved correct by modern analysis, the component parts of each, in the same proportions, being Silica, Alumina, and Glucina, coloured by the oxide of Chrome. Hence Phillips (Mineralogy : Beryl) states that " the only important difference between Emerald and Beryl is their colours ; which, since they present an uninterrupted series, is altogether insuffi­cient for a division of the present species." The Emerald is distinguished by its peculiar " emerald-green," which it derives from a small proportion of Chrome : all the varieties of other colours, tinged more or less yellow, or blue, or altogether colour­less, are Beryls. Yet, though thus identical in their chemical constitution, the Beryl is by far the harder of the two, its hardness being denoted in the scale by 7-5 to 8, and therefore even superior to that of the Garnet. It appears also to be of a singularly compact texture, for antique intagli in Beryl are found retaining their original surface-polish more perfectly than those in almost any other material. Not so the Emerald.
This gem held the same degree of rarity amongst the Romans as the true Smaragdus itself, for it was then obtained from India almost exclusively, " being rarely found elsewhere " (Plin.). Dionysius Periegetes enumerates it amongst the gems gleaned by the Indians from amongst the pebbles of their torrents, and as embedded in serpentine rock in Babylonia. Pliny distinguishes its varieties with all the accuracy of a modern mineralogist. The most admired, says he, emulate the green tint of pure sea-water (the modern Aquamarine). Next in favour is the Chrysoberyl, in which this green is tinged with a golden lustre (this probably is our Indian Chrysolite). There was a still paler