Page:Transactions of the Geological Society, 1st series, vol. 2.djvu/356

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Mr. William Phillips on the Oxyd of Tin.

neglect them in early life, which I have now occasion to regret, not only as it forbids the pursuit of mineralogy to an extent which alone would have enabled me to illustrate its objects in a manner wholly pleasing and satisfactory, but also as it renders me incompetent to reap the pleasure and instruction, which the works of those celebrated men the Abbé Haüy and the Count de Bournon, are calculated to convey. It must of course follow, that the only evidence I can offer in regard to the admeasurement and value of the angles of crystals, must be wholly mechanical.

I have given much attention in the endeavour to ascertain precisely the value of the angles of this substance, by the help of that admirable instrument the reflecting goniometer of Dr. Wollaston, having been previously assisted in its use by some hints and per-

    conceive to be chalcedony of a still lighter blue, though where most free from those veins, the general colour and appearance considerably resembles the chlorophane already described. It seems to have formed the principal part of a vein, being accompanied on each side by decomposing fluor, which has an ochreous crust similar to the gossan of the mines. On being placed on a live coal it gives a green light, nearly as splendid as the chlorophane, and does not fly; but flies when placed in the tire. It scratches glass easily.

    Another kind of fluor also encloses tin, which is of a light but dull brown colour, and greasy lustre, and is somewhat transparent at the edges. Its fracture is shattery. It gives nearly the same light as the chlorophane, but flies in the fire, though not when placed on a live coal. One specimen, about an inch in thickness, has on one side, a smaller vein of fluor, enclosed between two minute veins of chlorite, and on the other side, compact white fluor; attached to each side, is a. blue schist, the country of the mine. From the numerous crystals of tin imbedded in some specimens, I am induced to believe that it ran beside tin in the vein.

    I found also several other singular varieties of fluor, much harder and more compact than fluor generally is, of which the fracture is shattery and the colour purplish. When placed on a live coal, some of them begin by giving a greenish light, which soon changes to purplish, and afterwards ends in a dark purple. Others, give only a purplish light, and these do not fly even in the fire. Others give only a light green when placed on a coal, without dying, but fly when placed in the tire.