'9'4.I HYDROUS CALCIUM VANADATES. 51 



proximatetly correct, and may be several degrees in error, owing to 

 the weakness of the lithium light source used, and consequent lack of 

 sharpness of position of total extinction. 



The above optical data indicate that this mineral is in all proba- 

 bility monoclinic in crystal system, with its optic axial plane normal 

 to the plane of symmetry. To summarize, the determinative optical 

 characteristics of this mineral are: Crystal system, probably mono- 

 clinic; axial ratio, unknown; cleavage, poor and probably after oio. 

 H, about 2.5 ; sp. g., about 2.46. Color, dark red-orange to yellow- 

 orange ; luster, vitreous to sub-adamantine. Pleochroism, notice- 

 able, y^ orange; ^ = cadmium-yellow ; a = light cadmium-yellow. 

 Absorption, y>/3>a. Refractive indices, a= 1.775 ± .005 ; iS = 

 1. 81 5 ±.005; y= 1.825 ± .005. 



Birefringence is strong. 2VNa=50°.5 ± i. 2ENa about 100°. 

 2V u = 56° ±: 3°. ; 2E Li about 115°. Dispersion, crossed and strong, 

 Optical character — . Plane of optic axes normal to plane of 

 symmetry. 



On the whole, the material is homogeneous and comparatively 

 free from inclusions and suitable for chemical work. Here and 

 there foreign material was observed, but in the material selected for 

 chemical analysis it was not present in sufficient quantity to veil seri- 

 ously the chemical relations. 



Pascoite melts readily, forming a deep red liquid, and is easily 

 soluble in water. 



Analysis of Pascoite. 



Per Cent. Mol. Ratio. 



V=05 64.6 318 



M003 .3 — 



CaO 12.6 2.00 



H,0 100° — 13.8 6.87 



H.O 100° -f 7.8 3.88 



Undet. and loss 9 



1 00.0 



The ratios are not as satisfactory as could be desired. The values 

 approach those required from the formula Ca^VgOi^-iiHoO, which 

 calls for: V2O5, 63.76; CaO, 13.10; HjO, 23.14. Very recent tests 

 show that almost no loss of water occurs at room temperatures until 



