The Sapphire is not so easy to imitate, as its hardness exceeds that of the ruby, and imitations containing its known constituents, or of glass, are invariably softer than the natural stone. As before remarked, almost any form of corundum other than red is, broadly, called sapphire, but giving them their strictly correct designations, we have the olivine corundum, called "chrysolite" (oriental), which is harder than the ordinary or "noble" chrysolite, sometimes called the "peridot." The various yellow varieties of corundum take the name of the "oriental topaz," which, like most, if not all, the corundum varieties, is harder than the gem which bears the same name, minus the prefix "oriental." Then we have the "amethyst" sapphire, which varies from a red to a blue purple, being richer in colour than the ordinary amethyst, which is a form of violet-coloured quartz, but the corundum variety, which, like its companions, is called the "oriental" amethyst, is both rarer and more precious. A very rare and extremely beautiful green variety is called the oriental emerald. The oriental jacinth, or hyacinth, is a brown-red corundum, which is more stable than the ordinary hyacinth, this latter being a form of zircon; it changes colour on exposure to light, which colour is not restored by subsequent retention in darkness. The blue sapphire is of all shades of blue, from cornflower blue to the very palest tints of this colour, all the gradations from light to dark purple blues, and, in fact, so many shades of tone and colour that they become almost as numerous as the stones. These stones are usually found in similar situations to those which produce the ruby, and often along with them. The lighter colours are usually called females, or feminine stones, whilst the darker ones are called masculine stones. Some of these dark ones are so deep as to be almost black, when they are called "ink" sapphires, and if inclining to blue, "indigo" sapphires, in contradistinction to which the palest of the stones are called "water" sapphires. The colouring matter is not always even, but is often spread over the substance of the stone in scabs or "splotches," which rather favours imitation, and, where this unevenness occurs, it may be necessary to cut or divide the stone, or so to arrange the form of it that the finished stone shall be equally blue throughout. In some cases, however, the sapphire may owe its beauty to the presence of two, three or more colours in separate strata appearing in one stone; such as a portion being a green-blue, another a cornflower blue, another perfectly colourless, another a pale sky blue, another yellow, each perfectly distinct, the stone being cut so as to show each colour in its full perfection.