PROCEEDINGS OF THE NATIONAL MUSEUM. 



VOL. 60. 



stances crudely rectangular, their borders coinciding with the cleav- 

 age and parting of the surrounding velardeiiite. In less amount 

 there occurs intergrown with the garnet and also disseminated in 

 grains in velardeiiite, another isotropic mineral having a pale brown 

 color in thin section. This has an index of refraction slightly lower 

 than that of the garnet and is doubtless spinel. The total volume 

 of the minerals other than velardeiiite in the specimens is less than 

 5 per cent of the whole. The only other mineral identified is mag- 

 netite, which occurs in disseminated euhedral grains. 



OPTICAL PROPERTIES. 



The velardeiiite is colorless as seen under the microscope. It is 



uniaxial and negative. The indices of refraction as determined by 



immersion are : 



o) = 1.657±.002 



£=1.653 ±.002 



a)-e= .004±.002 



In thin section the mineral polarizes in grays, in sections of approxi- 

 mately .03 mm. thickness. Where garnet occurs in the velardeiiite, 

 however, there is a halo in the velardeiiite around the garnet grains 

 which has higher birefringence as though some constituent of the 

 garnet had diffused into the other mineral for a short distance and 

 had increased its birefringence. 



CHEMICAL PROPERTIES. 



The mineral is readily soluble in acids with separation of gelat- 

 inous silica. Pure material for analysis was secured by separation 

 with heavy solutions. Upon analysis this purified material gave 

 the results tabulated in column 3 below. In colunm 2 are given the 

 figures obtained by E. T. Allen upon the material from Velardeiia, 

 Mexico, described by Wright.^ 



Atialyses of Velardenite from California and Mexico. 



SiO,.. 

 TiO;.. 



A1203. 

 Fe.,03 



FeO.. 

 MnO. 

 MgO. 

 CaO.. 

 Na,0. 

 K,0.. 



n,o.. 



(n 



California. 



27.88 



25. 52 



L59 



.43 



4.18 

 40.86 



34 



100. 80 



(2) 

 Mexico 



26. 33 



.03 



27.82 



L43 



.50 



.01 



2.44 



39.55 



.21 



.10 



L85 



100. 27 



1 Wright, F. E., Amcr. Journ. Science, vol. 26, p. 547, 1908. 



