188 THE ROYAL SOCIETY OF CANADA 



lately bordering the spheres, is clouded and bluish as compared with 

 that further distant. There seems to have been some reaction be- 

 tween the chalcedony and the ferrierite, and it is possible that at the 

 time the crystals of the latter mineral were forming, the surrounding 

 silica had not yet assumed the solid state, but was still in the gelatinous 

 condition. 



The mineral has a hardness of 3 to 3^, and the specific gravity 

 is 2-150. 



Optical Characters 



The blades show straight extinction when lying flat, on a(lOO), 

 and also when they rest on 5(010) and on c(OOl) ; in each case com- 

 pensation takes place when the quartz wedge is inserted normal to 

 the length, whence it appears that the a-axis = a, 6-axis = /?, c-axis = Y, 

 and the axial plane lies in the direction of elongation of the blades. 

 In convergent light it is seen that the obtuse bisectrix is normal to 

 the blades, or coincides with the a-axis and therefore = a, and the 

 birefringence, which is weak, is thus positive. 



The refractive indices /? and y were determined by total reflection 

 from a(lOO), the crystal being immersed in methylene iodide, and the 

 obtuse optic axial angle was measured in the same medium. The 

 angle 2V calculated from the latter measurement, the indices /? and 

 Y, and the index a calculated from these values, are as follows: — 



2V = 50°25'; a=l-478, /3 = l-479, r=l-482, T-a = 0-004. 



It was necessary to employ very small plates for the deter- 

 mination of the refractive indices, because in the larger blades, the 

 face a(lOO) is never a perfect plane. It is believed, however, that 

 the values given above are approximately correct. 



Chemical Composition 



Heated in the flame of a bunsen burner, the mineral whitens, and 

 thin splinters fuse to a blebby glass. Fusibility 3 — 3^. The flame 

 is yellow, and observed with the hand spectroscope it shows only the 

 sodium line. Heated in a closed tube, the mineral whitens and gives 

 off much water, which is slightly acid. Insoluble, or only very slight- 

 ly soluble, in hydrochloric acid. 



In view of the danger of contamination with chalcedony, especial 

 care was taken in selecting the material for analysis, and colourless 

 and perfectly transparent blades only were used. The fusion was- 

 very pale bluish-green, indicating the presence of a trace of manganese. 

 The analysis gave the following result: — 



