NDGREN 
[ILLEBRAN 
:n and"] 
RAND. J 
51 
iew of the ease with which most of it is expelled, leads to an ortbo- 
ilicate ratio— R' 22 R" 2 R'" 6 (SiOJ"" n . 
On the whole, considering also the bad summation of the analysis, 
; is more rational to regard the mineral as a hydration product of an 
riginal metasilicate molecule than to attempt to construct a complex 
fcmula which could have but a very doubtful value. As the mineral 
i not a mixture, but is optically well individualized, we have, after 
3me hesitation, thought best to designate it by the name morencite, 
erived from the locality in which it was found. 
LIBETHENITE. 
This hydrous, basic phosphate of copper (H 2 Cu 4 P 2 O 10 ) was found 30 
set below the adit level of the Coronado lode, in the main shoot. It 
i a matter of interest to record its occurrence, for this rare mineral 
as never before been noted in the United States. It occurs in small 
rystals, less than 1 mm. in length, deposited in cavities and seams in 
quartzite gangue. The mineral was identitied by 
of. S. L. Penfield, who also kindly measured and 
gured the crystals. Professor Penh'eld describes 
le occurrence as follows: 
The only associated minerals are occasional clusters of un- 
ite quartz crystals and small tufts of radiated malachite 
>edles. The color of the libethenite varies from lio-ht to 
irk olive-green, depending upon the size of the crystals. 
le habit of the crystals, as shown by the accompanying 
ustration, is a combination of the prism m (110) and brachy- 
fme e (Oil), which is exactly like that commonly observed 
libethenite from foreign localities. On an occasional crystal 
} brachypinacoid b (010) was also observed. Although the crystals are brilliant, 
lie faces are generally vicinal and give uncertain or multiple reflections of the 
[niometer signal. The best reflections were obtained from the faces of the dome r, 
d three measurements of e e', Oil Oil gave 69° 52', 70° 18 / , and 70° 14'. The 
t measurement, obtained from the best reflections, is close to the value, 70° 8', 
tained by Kose. The best measurements of the prismatic angle gave m ^ m" ', 
I) ^ ll0= 87° 11 / , which, considering the vicinal character of the prismatic faces, 
ijreasonably close to the value of Rose, 87° 40', as given in Dana's Mineralogy. 
iffemall crystal resting on a prismatic face, when examined in convergent polarized 
lint, showed an optical axis nearly in the center of the field, with the dark bar 
jr|;ining at right angles to the vertical axis, thus indicating that the optical axes are 
l^the plane of the base, as determined by Des Cloizeaux. The presence of copper, 
iter, and phosphoric anhydride was determined by chemical tests. 
'\ more detailed search would probably reveal small quantities of 
posphates from other mines near Morenci. They arc certainly not 
a.mdant. 
Fig. i.— Libethenite. 
