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Page:Popular Science Monthly Volume 4.djvu/463

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THE SPANG COLLECTION OF MINERALS.

color is a translucent green—in most other recorded cases it is yellow or brown.

One of the most curious specimens is a natural amalgam of silver. It is a dodecahedral crystal, one-half an inch by three-eighths in size, which communicates, by a solid rod of the same material passing through the interior of the rock and nearly concealed from view, with a similar crystal of amalgam. When placed in such a position that one crystal is vertically above its mate, and allowed to stand for a short time, the mercury finds its way downward and distends the lower crystal until its faces are quite obliterated. In fact, it is converted into a pear-shaped drop, and looks as if it were about to fall from the crystal. When the specimen is inverted and allowed to remain so for half an hour, the mercury percolates through the solid mass of amalgam, the distended crystal acquiring its former definite outlines, and settles into a drop depending from the apex of crystal No. 1. This lusus naturæ, an hour-glass of metallic crystals, is, I believe, without parallel.

Then there is a resplendent crystal of axinite from Switzerland, among multitudes of others, which is three inches upon one of the faces and four inches measured along its greatest dimension; and a cluster of stibnite crystals from Hungary, weighing perhaps five pounds, of which the largest crystal is a prism three inches long and three-eighths of an inch thick, perfectly terminated.

In conclusion, the emeralds deserve our admiration, as they would that of persons least sensible of natural beauty. Of these, there is a number of large crystals, some mounted upon the rock in which they occur, others detached. Some of the latter from Bogotá have highly-modified terminations. Although not so large as the others, being but one-half an inch in length and three-eighths of an inch in thickness, by far the finest emerald is one which is implanted, along with smaller crystals, upon a piece of rock from the Ural Mountains. It has a perfect termination, presenting very many rhombohedral and pyramidal planes. Without a flaw, absolutely limpid, and of wonderful purity and depth of color, it is a natural gem, in the eyes of a mineralogist incomparably more beautiful than any cut and polished jewel could be. Its history might suggest to the writer of fictions some features of a romance, it having been given by a Czar of Russia to Taglioni, and subsequently placed by her in pawn with a wealthy gentleman in Paris.