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90 The smaragdus of Theophrastus included with the beryl a number of quite different stones, such as the chrysocolla and dioptase. Pliny's smaragdus included, besides the above, the green chrysoberyl and the chrysoprase, as well as the green plasma, the prase, and green jasper. In native East Indian jewellery the emerald is usually cut en cabochon; this form conceals the flaws to a great degree. In Europe the step-cut is considered the most suitable style. Emeralds are occasionally engraved or carved. In the Hope collection there was a beautiful vinaigrette made out of two emeralds, ⅞ inch in height, and ⅞ inch across; it brought 145 guineas when sold by auction in 1886.

The cymophane or true cat's-eye, the hard specimens called oriental chrysolite by jewellers, and the alexandrite are varieties of chrysoberyl. Their differences of hue and of physical appearance are not associated with any essential differences of composition. The colours of chrysoberyl range from columbine red through brownish yellow to leaf green; a golden yellow and a greenish yellow are not unusual. The coloured chrysoberyls are strongly dichroic; some brownish specimens from this cause may present to the unassisted eye the aspect of tourmalines. The green leaf, or deep olive green variety, known as alexandrite, of which fine flawless specimens of large size have been sent from Ceylon, is remarkable for appearing of a raspberry red hue by candle or lamplight. This mineral crystallises in the orthorhombic system; twins are frequent. The hardness of chrysoberyl approaches that of the sapphire: it is 8.5. Its lustre and brilliancy are considerable. Its specific gravity averages 3.7; it is but slightly lowered by strong ignition.