The oldest mines, which up to quite a recent date were the only extensive deposit of opal known, were at Cserwenitsa, near Kashau, in Hungary. From them in all probability emanated the opals known to the Romans. The opals from this locality were generally quite small, and large pieces were rare and commanded high prices. The Hungary mines, however, proved quite unable to compete with the rich fields at White Cliffs, New South Wales, in spite of the efforts that were made to depreciate and exclude from the market the new stones, and at the present time few of the opals on the market come from them. As so often happens, the White Cliffs deposit was discovered by accident. In 1889 a hunter, when tracking a wounded kangaroo, chanced to pick up an attractively coloured opal. The district is so waterless and forbidding that, but for such a chance, the opals might have long lain hidden. They occur in seams in deposits of Cretaceous Age in a variety of ways, filling cavities in rocks or sandstones, or cracks in wood, or replacing wood, saurian bones, and some spiky mineral, which may have been glauberite. In recent years, another rich deposit was discovered farther north, on both sides of the boundary between Queensland and New South Wales. The field is remarkable for the darkness of its opals, which are called ‘black opal’ in contradistinction to the lighter-coloured stones previously known. From Lightning Ridge in New South Wales come stones stained deep black which quite merit the designation black opal. The sandstone in which they are found is rich in iron, and this is no doubt responsible for the deepness of their tint. Mexico is noted for the fire-opal, which is found at Esperanza, Queretaro, and Zimapan; but other kinds of opal also are found at these places. [Illustration: _PLATE XXVIII_ OPAL MINES, WHITE CLIFFS, NEW SOUTH WALES] The price of opal varies greatly, according to the intrinsic colour and the uniformity and brilliance of the opalescence. Common opal can be bought at as low a rate as 1s. a carat, while black opal ranges from 10s. to £8 a carat; but a good dark stone displaying a flaming opalescence commands a fancy figure, fine stones of this class being exceedingly rare. Fire-opal enjoys only a limited popularity now, though a few years ago it was in some demand; the price runs from 2s. to 10s. a carat. CHAPTER XXXI FELSPAR (_Moonstone, Sunstone, Labradorite, Amazon-Stone_)