Louderback. — Benitoite. 



153 



axis is yellowish brown or ocreous yellow to reddish brown, the 

 one perpendicular to this light yellow, absorption c'> a' in which 

 C' lies nearest the prism axis. The refractive index is high — at 

 least greater than that of monobromnaphthalene, 1.654. 



The name carlosite is suggested for this mineral, from the 

 nearby San Carlos peak, one of the highest points of that part of 

 the range. 



Benitoite and carlosite occur as individual disseminated crys- 

 tals in narrow veins in a basic igneous rock or in a schist which 

 has been considerably altered by the solutions that formed the 

 veins. The benitoite is apparently restricted to the veins, the 

 carlosite also occurring in the neighboring parts of the wall rock. 

 The chief gangue of the veins is a soda rich zeolite. The prop- 

 erties of carlosite and the nature of the gangue were determined 

 on small and unsatisfactory quantities, as the collectors were 

 interested in the supposed sapphires and not in its matrix. The 

 writer has recently been able to collect specimens of the matrix 

 and crystals of carlosite and expects shortly to make a more 

 extensive report on the properties of benitoite and carlosite, their 

 paragenesis, etc. 



Issued July 30, 1907. 



