Vol. 5] 



Louderback. — Bcnitoitc. 



377 



P measured from c as pole face 



/>i 76° 35' p 1 striated blurred reflection 



p2 train 72° 56'-76° 20' pi 103° 22' supplem. 76° 38' 



76° 24' p3 striated, blurred band of light 



pi 76° 30' p* 103° 22' supplem. 76° 38' 



c as pole face 



/)i 103° 15' supplem. 76° 45' 

 p2 103° 31' to 40' supplem. 76° 20-29' 

 pa 103° 10' supplem. 76° 50' 

 p* 103° 12' supplem. 76° 48' 

 average p=76° 37' 

 extremes 76° 20'-70° 50' 



2<£ measured 94° 52', 94° 43', 05° 01', 94° 47'. 

 Average 94° 51' or 0=47° 25'. 



The pinacoid a was found on this crystal as a minute rhombus 

 truncating the front and back solid angle of the four p faces, the 

 signal was very faint and could not be set within S or 10 minutes. 



<P p 

 Measured 89° 50' 89° 42' 



Calculated 90° 00' 90° 00' 



Cleavage is not distinct but appears to exist parallel to the 

 basal plane and even less distinct perpendicular to it (possibly 

 parallel to the two pinaeoids) . "Whenever cleavage cracks appear 

 under the microscope, the extinction is always straight with 

 respect to them. 



The optical orientation is n=a, b=b, c— c. c is the acute bi- 

 sectrix and in convergent light in sections perpendicular to the 

 acute bisectrix (basal section), the optic axes emerge just at the 

 edge of the field. 



The refractive index is high (>1.73) and the double refrac- 

 tion strong. The mineral is transparent and has a honey .yellow 

 to brownish yellow color in fair sized fragments, very pale and 

 transparent in thin section. In thicker pieces pleochroism is 

 visible, c ocreous or reddish yellow, b light yellow, a similar to b 

 but slightly paler. Absorption c>t>>tt. Hardness greater than 

 glass (5.5) ; density determined on the largest crystal, between 

 3.85 and 3.9. Heated in closed tube it becomes, paler colored, 



