376 



University of California Publications. 



[Geology 



Joaquinite. Associated with the minerals of the benitoite- 

 bearing veins is occasionally found a honey yellow or light brown 

 substance in small generally individual crystals or crystal grains 

 rarely over one millimeter in diameter which is believed to be a 

 new mineral. On account of its rarity, minute size and the general 

 imperfectness of its crystals, its investigation has been attended 

 with considerable difficulty. A preliminary statement of its 

 properties is here presented. Some recently acquired material 

 containing this mineral is being worked over for its separation 

 with a view to a more complete study and for . purposes of a 

 quantitative chemical analysis which has not heretofore been pos- 

 sible and the writer expects to present a more complete descrip- 

 tion of the mineral in the near future. 



The crystals are generally equant, occasionally slightly 

 tabular, and always show two parallel almost square smooth faces, 

 the other larger faces being strongly striated. The evidence so 

 far obtained indicates that the mineral is orthorhombic and the 

 two broad smooth faces are taken as the basal plane, and the eight 

 lateral inclined planes, the only pyramidal planes so far observed, 

 are taken as the unit pyramid. We have the combination c(001) 

 and p(lll) and on one crystal o(100). The axial ratios based on 

 the position angles for p of ^>=76° 37', p=47° 25' are a-.b:c= 

 2.8440:1 :0.9190. 



ELEMENTS. 



a=0.9190 | lg 



a=9. 96332 



lg «.,= 



9.50939 



lg P«= 



0.49061 



a„=0.3231 



p„=3.0946 



c=2.8440 | lg 



c=0. 45393 





9.54607 



lg 7o= 



=0.45393 



6 o =0.3516 



2o=2.8440 



Two crystals and part of a third were studied goniometrically, 

 I )iit only one of the crystals was satisfactory. Measurement is 

 interfered with in two ways. The basal faces are commonly some- 

 what curved (concave), and the pyramid faces are strongly 

 striated horizontally. As a result measurements could not be 

 trusted on two of the crystals within one or two degrees. On one 

 of the crystals the basal faces are quite plane and can be set very 

 satisfactorily within a few minutes, and the majority of the 

 pyramid faces show plane strips broad enough to get definite 

 reflections. For this crystal I am indebted to Mr. R. M. Wilke 

 of Palo Alto. 



