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jasper, amethyst, quartz and agates

AGATE. A mineral whose basis is calcedony, blended with variable pro portions of jasper, amethyst, quartz, opal, heliotrope, and carnelian. Ribbon agate consists of alternate and parallel layers of calcedony with jasper, or quartz, or amethyst The most beautiful comes from Liberia and Saxony ; it occurs in porphyry and gneiss. Brecciated agate is of Saxon origin ; it has a base of amethyst, containing fragments of ribbon agate, constituting the beautiful variety. Fortification agate, found in Scotland and on the Rhine, is in nodules of various shapes, imbedded in amygdaloid. On cutting it across, and polishing it, the interior zig-zag parallel lines bear a considerable resemblance to the plan of a modern fortification. In the very centre, quartz and amethyst are seen in a splintery mass, surrounded by the jasper and calcedony. Mocha stone, from Mocha, in Arabia, where it is chiefly found, is translucent calce dony, containing dark outlines of arborization, like vegetable filaments. Moss agate, so called from its ramifications of a vegetable form, is a calcedony, variously coloured, and occasionally traversed with irregular veins of red jasper. An onyx agate set in a ring belonging to the earl of Powis, contains the chry salis of a moth. Agate is found in most countries, chiefly in trap rocks and serpentine. The oriental agate is almost transparent, and of a vitreous appear

ance. The occidental is of various colours, and often veined with quartz or jasper. Agates are most prized when the internal figure nearly resembles some animal or plant. Agates are artificially coloured by immersion in metallic solutions. They are extensively used in Paris for making cups, rings, seals, handles for knives and forks, sword hilts, beads, smelling bottles, snuff boxes, &c. At Oberstein, on the Rhine, where the stones are abundant, they are cut and polished on a considerable scale, and at a very moderate price. The surface to be polished is first coarsely ground by large millstones of a hard reddish sand-stone, moved by water. The polish is afterwards given on a wheel of soft wood, moistened and imbued with a fine powder of hard red tripoli, found in the neighbourhood. Antiquaries use the term agate to denote a stone of the kind engraved by art. In this sense agates make a species of antique gems, in the workmanship of which we find eminent proofs of the great skill and dex terity of the sculptor. Several agates of exquisite beauty are preserved in the cabinets of the curious.