14 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 74 



Analysis of augite {92150) from Cerro Mo'cado 

 Forest A. Gonyer, analyst 



MnO , None. 



K'O 0. 05 



Na20 1. 86 



H.0 . 19 



100.77 



SiO , 50. 97 



TiO.' . 20 



FeO 6. 96 



Fe^Os 7. 08 



AUO3 . 95 



CaO 20. 96 



MgO 11. 55 



The mineral is therefore essentially diopside with minor amounts 

 of the hedenbergite and acmite molecules. The mineral composi- 

 tion, calculated from the above analy- 

 sis, is: 



Diopside 65. 



Hedenbergite 22. 8 



Acmite 11. 



Magnetite 1. 2 



100. 00 



Sepiolite. — In Socavon No. 2 occurs 

 a white mineral made up of very fine 

 fibers matted into light masses (92157, 

 92158). The writer has been told by 

 some of the worlanen that masses of 

 this mineral several feet in diameter 

 have been encountered. This mineral 

 proves to be sepiolite. An analysis 

 of this material, essentially pure as 



determined under the petrographic microscope, yielded the following 



results : 



Analj/sis of sepiolite (92158), from Cerro Mcreado 

 W. F. Foshag, analyst 



Fio. 3. — Crystal Habit of Aogitb 



CaO 0. 24 



MgO 22. 95 



99.57 



H2O (— ) 8.60 



ao (-I-) 10.20 



SiOa 55. 34 



AI2O3 1. 81 



FeW . 43 



Under the microscope the sepiolite is so finely fibrous that the pre- 

 cise optical proj^erties can not be determined. The mean index, how- 

 ever, was found to be 1.52, which corresponds Avell with that of ordi- 

 nary sepiolite. 



Sepiolite is later than the martite and, since it incloses broken 

 crystals of apatite, is later than this mineral as well. Associated 

 with it is quartz that is obviously later than the sepiolite. 



