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XII
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CHRYSOBERYL
The chemical constitution of the chrysoberyl was long in doubt. Its composition was differently described by analysts, some of whom undoubtedly confounded it with varieties of the chrysolite. With the errors made, however, the presence of one constituent after another was demonstrated, until the various elements and their proportions became definitely known. It is composed of nearly eight-tenths alumina, a little less than two-tenths glucina, and a small proportion of ferrous oxide, which differs with the varieties.
In hardness it is inferior only to the corundums, but it seldom approaches the precious or many of the semi-precious stones in beauty of coloring. The common variety is usually pale yellow, greenish-yellow, or yellowish-green. In the latter shade it resembles the chrysolite, and is often so called. Sometimes it is golden yellow and golden brown, occasionally a columbine red or pale olive-green, similar to the ordinary day and night colors of the alexandrite variety. Heat does not change the color.
The lustre is vitreous, but somewhat oily, and some show an internal bluish opalescence.
It is found usually as rolled pieces in river gravels, with the diamond in Brazil, with tourmaline, sapphire, and spinel, in Ceylon, and among the pebbles of Burmah and Borneo. It is often associated with topaz and the corundums, and with emeralds in the Tokowoia mines east of the Urals. Well-formed crystals have been found with aquamarine and garnet in Connecticut granite. A few very beautiful specimens of the alexandrite variety from the latter State were reported some years ago by Mr. E. Passmore, of Boston. It also 108
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