PALACHE AND SCHALLERI HODGKINSONITE 475 



crystal faces but in reality determined in their outline almost 

 wholly by the older platy barite which encloses them. The clear 

 pink color and brilliant cleavage of hodgkinsonite, together with 

 the snow white barite make such specimens both striking and 

 attractive in appearance. One mass of ore with a surface 20 cm. 

 square is at least half covered with hodgkinsonite. In one case 

 only has such a vein been found in which the angular cells formed 

 by the intersecting barite plates were not wholly filled by hodg- 

 kinsonite so that the latter was free to develop crystal planes. 

 From this specimen three crystals of good quality were detached 

 and these served to establish the axial ratio of the species. 



Other crystals were found occupying cavities in thicker veins 

 free from barite. These crystals, the largest 1 cm. long, were 

 much affected by solution, the faces being generally dull or 

 facetted. They were accompanied by black rhombohedral crys- 

 tals of pyrochroite and scalenohedral crystals of calcite, both 

 later in age and encrusting hodgkinsonite. The latter is im- 

 planted directly on willemite or franklinite and in one specimen 

 on manganese garnet. The association and mode of occurrence 

 both indicate a pneumatolytic origin for the new mineral. 



Hodgkinsonite is monoclinic with normal symmetry. The 

 highly perfect cleavage, normal to the symmetry plane, has been 

 taken as the basal pinacoid. The elements were calculated from 

 the angles of the forms taken as (110), (Oil), and (221) together 

 with the inclination of the cleavage (001) to the prism zone. 

 These angles follow. 



(001)=^ _ o .-,_i, > Average of 2 readings on 2 crystals. 



(11^) "1 _ ' „_, )> Average of 7 readings on 3 crystals. ' 



f <p = 4° 42' 1 

 {011)n _ o , /i i\.verage of 2 readings on 1 crystal. 



(221) ■> _ , > Average of 4 readings on 2 crystals. 



The axial elements thus calculated are: ' 



Po = 0.7254 qo = 1.1114 /x = 84° 33J'. 

 a :b :c = 1.539 : 1 : 1.1165 = 84° 33^'. 



