458 Lindgren and Hillebrand — Minerals from Arizona. 



center of the field with the dark bar running at right angles to 

 the vertical axis, thus indicating that the optical axes are in 

 the plane of the base, as determined by Des Cloizeaux. The 

 presence of copper, water and phosphoric anhydride was deter- 

 mined by chemical tests." 



A more detailed search would probably reveal small quanti- 

 ties of phosphates from other mines near Morenci. They are 

 certainly not abundant. 



Brochantite (H 6 Cu 4 SO 10 ). — This basic sulphate of copper is 

 usually supposed to be one of the rarer minerals. It was, 

 however, discovered at a few places near Metcalf and 

 Morenci, in well developed crystals, and this led to a syste- 

 matic microscopic examination of the green ores, hitherto sup- 

 posed to be malachite. The result was surprising, as the 

 mineral was proved to be of extremely common occurrence, 

 mostly intergrown with malachite, which had effectively 

 masked its presence. It is believed that a careful examina- 

 tion of many so-called malachites from other districts will dis- 

 close the overlooked importance of brochantite as a copper ore. 



Brochantite is frequently crystallized in the short but stout 

 rhombic prisms combined with dome and brachypinacoid char- 

 acteristic of the species. Needle-shaped and fiat crystals are 

 more rare. The crystals are usually of small size and fre- 

 quently microscopic. It occurs as lighter or darker emerald- 

 green crusts on limonite or sericitizecl porphyry from the Red 

 ore body in the Shannon mine, from the Metcalf mines and 

 many other places ; as fine-grained aggregates in altered 

 porphyry at the Shannon mine, near the surface, and constitu- 

 ting valuable ore with up to 30 per cent copper ; from crop- 

 pings of the King vein, filling seams and coating porphyry 

 fragments as flat pieces or even foils with almost pearly luster ; 

 from the croppings of the Copper Queen mine between 

 Morenci and Metcalf, here as flat stellar aggregates of bluish 

 green foils ; at many places near Morenci, as, for instance, 

 Copper Mountain and Montezuma mines, at the latter locality 

 replacing chalcocite. It would probably not be found absent 

 from any mine in the district containing oxidized copper ores. 

 Malachite often develops later than the brochantite. 



On the whole, the mineral is most abundant in fissure veins 

 in porphyry, though also occurring in the irregular deposits in 

 limestone. 



Brochantite has an excellent cleavage parallel to the brachy- 

 pinacoid. The macropinacoid is the axial plane and the acute 

 bisectrix is seen emerging in cleavage foils. Pleochroism very 

 slight. Birefringence much lower than malachite, about equal 

 to that of augite. This, as well as the absence of twins, dis- 

 tinguishes brochantite from malachite. The reaction for sul- 

 phuric acid is of course a valuable aid. 



