88 



ceptible. The light that vibrates perpendicularly to the vertical 

 axis is somewhat more strongly absorbed than the light vibra- 

 ting parallel to it. A section parallel to the base appears di- 

 vided into zones parallel to the hexagonal outline of the basal plane. 

 These zones are marked by different degrees of intensity of the 

 faint yellowish grey colour. In general the outer parts have a 

 higher colour than the central portions. The single zones 

 sometimes appear as hair-like lines and are most distinctly 

 defined. The mineral is uniaxial and the double refraction is 

 negative and weak. The material available has not been suited 

 for the determination of the indices of refraction. 



The mineral scratches calcite with difficulty. Its hardness 

 is, consequently, a little above 3. It has an eminent basal 

 cleavage, which gives to it the character of a mica or chlorite. 

 In a perfectly fresh condition, however, the mineral is not 

 so easily cleaved as in a somewhat altered state. The mineral 

 is very brittle and the cleavage laminae are neither flexible 

 nor elastic. 



The specific gravity, determined by weighing in benzole, 

 is 2,633. Before the blowpipe the mineral fuses slowly to a 

 clear and almost colourless glass. In the salt of phosphorus 

 bead it gives a siliceous skeleton. With the other fluxes it 

 reacts for iron and manganese. It is not attacked by acids other 

 than hydrofluoric acid. 



The analysis has been performed by myself. After drying 

 the material until the weight at 100° C. is constant, it loses 

 only about V4 °/o on strong ignition. This loss has been con- 

 sidered as «hygroscopic« moisture not driven off at 100° and 

 has not, therefore, been taken into account. The degrees of 

 oxidation of the iron were determined after decomposing the 

 mineral with dilute sulphuric acid and cryolite powder in a tube 

 closed at both ends. Owing to the insufficient supply of material 

 no test for fluorine could be made. The result of the analysis 

 is as follows. 



