Lindgren and Hillebrand — Minerals from Arizona. 457 



probable formula, whereas if all water is excluded the ratio is 

 that of a metasilieate — ~R"J&"\ (Si0 3 ) // 11 . On the other hand, 

 to include the whole of the water as essential to the silicate 

 molecule, for which there is little ground in view of the ease 

 with which most of it- is expelled, leads to an orthosilicate 

 ratio— E' 22 R // 2 R /// 6 (Si0 4 ) /, ; / 11 . 



On the whole, considering also the bad summation of the 

 analysis, it is more rational to regard the mineral as a hydration 

 product of an original metasilieate molecule than to attempt to 

 construct a complex formula which could have but a very 

 doubtful value. Considering that the mineral is not a mixture, 

 but optically well individualized, we have, after some hesita- 

 tion, thought best to designate it by the name morencite, 

 derived from the locality in which it was found. 



Libethenite (H 2 Cu 4 P 2 O ]0 ). — This hydrous, basic phosphate of 

 copper was found 30 feet below the adit level of the Coro- 

 nado lode, in the main shoot. It is a matter of interest to 

 record its occurrence, for this rare mineral has never before 

 been noted in the United States. It occurs in small crystals, 

 less than l mm in length, deposited in cavities and seams in a 

 quartzite gangue. The mineral was identified by Prof. S. L. 

 Pentield, who also kindly measured and figured the crystals. 

 Prof. Peniield describes the occurrence as follows : 



" The only associated minerals are occasional clusters of minute 

 quartz crystals and small tufts of radiated malachite needles. 

 The color of the libethenite varies from light to dark olive- 

 green, depending upon the size of the crystals. The habit of 

 the crystals, as shown by the accompany- 

 ing illustration, is a combination of the 

 prism m (110) and brachydome e (Oil), 

 which is exactly like that commonly ob- 

 served on libethenite from foreign locali- 

 ties. On an occasional crystal the brachy- 

 pinacoid b (010) was also observed. Al- 

 though the crystals are brilliant, the faces 

 are generally vicinal and give uncertain or 

 multiple reflections of the goniometer sig- 

 nal. The best reflections were obtained 

 from the faces of the dome 6, and three 

 measurements of e^e\ Oil ^ Oil gave 

 69° 52', 70° 18' and 70° 14'. The last measurement, obtained 

 from the best reflections, is close to the value, 70° S\ obtained 

 by Pose. The best measurements of the prismatic angle gave 

 m/^??^ /// , 110 /n 110 — 87° ll 7 , which, considering the vicinal 

 character of the prismatic faces, is reasonably close to the value 

 of Pose, 87° 10', as given in Dana's Mineralogy. A small 

 crystal resting on a prismatic face, when examined in con- 

 vergent polarized light, showed an optical axis nearly in the 



