Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/122

 it seems probable that both its colour and hardness may be ascribed to the dissemination of that substance throughout the mass, which leaves a black streak on paper. Some specimens also abounded with pyrites both arsenical and martial, and some of them have decomposed since they came into my possession. The veins of Tol Carn mine afforded little or no copper; the uranium was found in one of them at about 30 fathoms from the surface.

The colours of the crystals both from Tol Carn and Tin Croft mines are nearly the same. They vary from almost opake white to yellowish, and pass into the most brilliant yellow; some being transparent, others opake. Of some tabular crystals, the center is transparent and nearly colourless, and the edges are yellow. On other specimens the crystals are transparent and of a greenish hue, whence they pass through almost every shade, into deep grass green; while in others, the center of the crystal is yellow and the edges only are green. Again, from a brownish tinge they pass into a rich brown, but as the surfaces of these crystals glisten, the colour seems to be original; while on many specimens the crystals, which are of a light green colour, are hollow at their centers and of an ochreous brown, a circumstance arising doubtless from decomposition, and which in other specimens has proceeded so far as that the forms of the crystals can no longer be defined.

The crystals on some specimens from Tin Croft mine are accompanied by spiculæ of blue carbonated copper; in others, by green carbonated, and red and black oxides of copper, and on one specimen, they are deposited on minute spiculæ of oxide of iron. I have some specimens of the red oxyd of copper from the mine called Huel Jewel, on which there are very numerous and minute tabular crystals of the oxyd of uranium of a light green colour,