On Arborescent Native Copper in the Llandudno Mine, near Great Ormshead, North Wales

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It is well known that copper, like some other native metals, sometimes crystallizes in filiform and arborescent shapes; but in these forms they are mostly diffused through masses of mineral gauge, or spread out upon the matrix, apparently unable to bear their own weight. The symmetrical forms, however, to which we now refer are seen by a microscope to stand up like a crystalline grove of trunks and branches. The entire group is composed of separate crystals, strung out in axial lines; the crystals under high magnifying powers show the flat wedge-like octahedron; but there is no uniformity; each crystal, or spike of crystals, varies more or less in size and modification. In the small cavities containing these crystallizations, are associated crystals of ruby copper; the latter never run out into spikes or branching forms, but exist in single perfect or modified octahedrons, or are dotted about in irregular clusters of crystals. The whole of these minute crystallizations occur in a bed of brown limestone, yielding a soft, rich, yellow bisulphuret of copper, —the rich ore, however, being very intimately mixed up with the crystalline limestone, something like the material of a fine-grained granite or porphyry. The ore contained in this bed seems to be a medium or transition between the harder and more sulphureous ore of the bed below and the carbonates and oxides of copper of the bed above. The copper crystallizations here are peculiar to this bed alone, and are doubtless the result of the decomposition of