Crystallized Red Oxide of Copper

I have already figured some Cubical and Octaëdral Ruby Coppers. The present one from Cornwall is extremely rare and curious, as it has a remarkable modification—the cubo-octaëdron of Haüy, with the addition of an obtuse four-sided pyramid on each cubic face, formed as it were of somewhat distinct plates. In one crystal this pyramid is formed into a cross, the plates of which it is composed being notched or incomplete in the centre of their edges, and complete at the corners: see the right hand upper figure. With these crystals of similar forms, of very pure Copper, composed of oblong particles with a reticulated appearance, as if they were some of the others, of an anterior formation, having been deprived of their oxygen. These crystals are very extraordinary, as they comprehend the Octaëdron with truncated edges: they also truncated and bevelled solid angles, making a very compound crystal: see the left hand figure. The intermediate varieties are the dodecaëdron and octaëdron, truncated at the solid angles. The particles show some signs of being thread-like confused octaëdrons, somewhat resembling those on the following plate, tab. 147. They are externally between a copper colour and red, scarcely metallic in the lustre, until cut, and then perfectly so. It is, as the Count de Bournon observes, useful in many instances to use a magnifier to examine the crystals; and we should lose some very interesting beauties without it. These indeed may be pretty well seen by the eye alone, but it is admirable to observe how neatly these are formed by such help as the magnifying glass. We do not know of any other specimen of this kind.