Page:Popular Science Monthly Volume 4.djvu/462

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which consists of thousands of apophyllite crystals, many of them an inch and averaging half an inch in size, festooned about a cluster of pendant stalactites?

Two uncut diamonds of great brilliancy are remarkable for the perfection of their forms; one is an octahedron with dodecahedral planes, the other is an elliptic twin, in shape closely resembling a heart. Each stone is of one carat weight, and entirely limpid and without a flaw—fit, in fact, for setting, though never touched by the lapidary. Less costly, but hardly less beautiful than these, are some Aragonites from Sicily, which are strikingly thrown into relief by the pedestal of lemon-yellow crystals of sulphur upon which they are mounted. They are six-sided prisms, measuring two and a quarter inches along the vertical, and two and a half inches along the lateral axis. Their bases and summits are perfectly plane.

At the time of its purchase and incorporation into the museum of Harvard University, I had the pleasure of critically examining the collection of minerals which had been accumulated by Herr Liebner, a mining-captain in the Tyrol. The finest specimens were a suite of Tyrolese epidotes, and I imagined that Nature could not surpass them, until I saw those in the possession of Mr. Spang. Among others of still larger dimensions, there is one prism of epidote which is eight inches in length, and three-quarters by one half an inch in thickness. It is perfectly straight, and all its sides and terminal planes are of a smoothness and lustre indescribable. The light transmitted through the crystal in one direction is a magnificent ruby-red, almost identical in tint with that exhibited by light-red silver-ore. Another crystal might fairly be entitled a gem of immense size; it is three inches in length, and exhibits thirteen terminal planes. On revolving it into different positions, the light passing through it changes in color from a delicate hair-brown to cherry and then to deep ruby-red.

Before concluding this sketch, some bodies of extreme rarity should be mentioned, among them the chloro-carbonate of lead, termed phosgenite. Most mineralogists are rejoiced to obtain minute crystals of this mineral, the large crystals from Crawford, near Matlock, in Derbyshire, having sold for from fifteen to twenty pounds sterling each. This cabinet contains a perfect prism, of strong adamantine lustre on all its faces, which is one and a half inch in height, one and a quarter broad, and one and an eighth in thickness. Still more rare is a mineral, of which singularly enough we possess as yet no satisfactory analysis, known as Turnerite, from the Tavetsch Valley in the Alps. In this collection there is a number of perfect crystals, five if I remember correctly, each of which displays many highly-lustrous facets, and occurring both isolated and embedded in a rock made up of quartz and albite. The largest crystal is three-quarters of an inch long and five-eighths of an inch thick. It is a doubly-terminated hexagonal prism, the basal edges being regularly replaced by twelve small planes. The