PALACHE AND SCHALLER! HODGKINSONITE 



477 



a gram of small fragments which were later used for analysis. 

 The hardness is a very little less than 5. 



The optical characters have been only imperfectly determined. 

 The optic axial plane is parallel to (010). The mean refractive 

 index is 1.73, determined by the immersion method. The color 

 of the mineral varies from a bright pink to a pale reddish brown, 

 the luster is vitreous, the streak white. 



Fig. 1 



Fig. 1. Hodgkinsonite. Common habit of implanted crystals, showing basal 

 cleavage when removed from the matrix. Forms m(llO), s(Oll), r(221). On 

 etched crystals r is replaced by q{55'2) without change of habit. 



Fig. 2. Hodgkinsonite. Doubly terminated etched crystal. Forms: c(OOl), 

 m(llO), s(Oll), .t(305), g(552), m(322). 



The mineral decrepitates when held in the blowpipe flame, 

 wherein it fuses readily and quietly to a brown enamel. Heated 

 in a closed tube, hodgkinsonite decrepitates strongly, splitting 

 up into numerous thin cleavage scales which on further heating 

 yield water and become brown in color. The mineral is readily 

 soluble in acid, yielding gelatinous silica. 



The chemical analj^sis of hodgkinsonite was made on carefully 

 selected cleavage fragments of a clear pink color and gave the 



