406 W. jS. Yeates — Pseudomorjplis of Native Copper. 



writer, for identification. It had the appearance of copper; 

 but it was very brittle, and its specific gravity was much too 

 low for ordinary metallic copper, a fragment yielding only 

 4*1 5. The surface was, in part, made up of what appeared to 

 be tabular crystals, reminding one, in general form, of the 

 azurite crystals from the Copper Queen mine, in the adjoining 

 county of Cochise, Arizona, though the surfaces of the planes 

 were stippled, rendering only approximate measurements of 

 the angles possible. The surface of the specimen was coated 

 with a white clay-like substance, the most of which had been 

 cleaned off with a knife. This substance was found to be 

 kaolin. An examination of the fresh fracture with a lens 

 showed that the kaolin not only coated the surface, but that 

 it was intimately mixed with the copper-like particles, produc- 

 ing a granular fracture, and giving rise to the stippling on the 

 crystal surfaces. A fragment under the pestle in an agate 

 mortar was reduced to powder, the metallic grains, which had 

 been proved, before the blowpipe, to be copper, segregating 

 together, and marking the mortar and pestle with bright shin- 

 ing streaks. The copper being so finely divided, it was now 

 clear why the specimen was brittle, and why it had so low 

 specific gravity. If the copper was, as it appeared to be, a 

 pseudomorph after azurite, the latter must have lost its carbonic 

 acid and water in the presence of some reducing agent, prob- 

 ably volcanic gases thrown up from below, leaving the copper 

 in a spongy state, upon which the kaolin was deposited, and 

 forced by pressure, while in a soft ; semi-liquid condition, into 

 the pores of the sponge. 



With a view to determining whether or not this was true, 

 Mr. Lucas was requested to furnish additional specimens for 

 study, which he kindly did. Among them, were several, 

 which, he informed the writer, had been cleaned with brush 

 and water and a knife; the others were in the condition in 

 which they were taken from the mines. These last appeared, 

 externally, to be flattened nodules of kaolin, sometimes colored 

 reddish brown. On the two opposite flattened sides were 

 slickensides — -evidence of the pressure, which had forced the 

 kaolin into the copper sponge. With dental instruments, the 

 writer exposed a fine group of the crystals of one of the nodules, 

 the most prominent crystal being almost perfect, and simulat- 

 ing in form those azurite crystals flattened parallel with the 

 plane —1-i, so common at the Copper Queen mine. By 

 measurement with a contact goniometer the angle between the 

 broad plane and an adjacent plane, on the copper crystal, was 

 found to be identical with that of —l-i / \2 on a fine Copper 

 Queen azurite crystal in the Museum collection. 



Additional circumstantial evidence may be found in the fact 



