334	A POPULAR TREATISE ON GEMS.
	From the variety and beauty of its colors, it is known, when * cut, in trade, under the various names of false emerald, false amethyst, false ruby, and false topaz, according to the color it exhibits. It is mostly found in metalliferous veins, and very rarely in the newer formations. Its localities are in Baden, Bohemia, Saxony, St. Gothard, at Derbyshire and Devonshire, in England, and the United States, in the last of which countries it occurs of most beautiful colors in fine crystals; from a lately-discovered locality at Russy, in St. Lawrence county, State of New York, I have specimens of crystals two feet long and five wide. It is found in Illi­nois, seventeen miles from Shawneetown; Blue Ridge, Maryland; Smith county, Tennessee; at Franklin Furnace, and Hamburgh, New Jersey; Saratoga Springs, and at Alexandria, New York; Middletown and Huntingdon, Connecticut; Thetford and Southampton lead mines, Mas­sachusetts, and on the White Mountains, New Hampshire. Fluor spar is cut for ring-stones and shirt-buttons, and particularly in such forms as are intended to be substituted for other gems; in Derbyshire there have been large mills for grinding, cutting, and polishing the flour spar into vases, cups, obelisks, plates, candlesticks, &c, ever since 1765, and there are now more manufactories, principally at Derby. That fluor spar which may be called the nodular variety, and the colors of which run in bands or zones, is only found in a single mine near Castleton, Derbyshire, and is known by the technical name of Derbyshire-spar or Blue John; it is used for various ornaments, to be met with all over the world, in parlors or mineral collections. In order to heighten the various colors in the ornamental specimens, before they are polished, they are heated to a certain de­gree, when the dark spots, or tints, disappear, and the colored bands become more distinct, and assume a peculiar purple or amethystic hue.