104 



The size of the needles is quite slight; their length is al- 

 most 1 cm; one of the largest was measured to a breadth of 

 ca. 0*3 mm, a thickness of 0*06 mm, but most of them are 

 slill finer. 



The transverse section of the needles is almost completely 

 lenticular; the two sides are quite evenly curved, and each of 

 them gives in the goniometer an almost completely continual 

 series of reflections, without any single surface being especially 

 conspicuous; each series of reflections has an extent of 70 — 

 90°; in the interjacent parts of the zone absolutely no reflections 

 are found. At the ends of the crystals surfaces are never 

 developed. 



The needles are of a bronze-yellow colour, highly shining; 

 the colours of absorption are about the common ones: 

 a dark reddish brown, 

 b yellowish brown, 

 с a little lighter yellowish brown. 



When placed on the cleavage faces the crystals show in 

 converging light a distinct axial image; the axial plane is 

 parallel to the longitudinal direction of the needles. The axial 

 angle has in glass hemispheres been determined to: 



2П = 104°. 



If the index of refraction of the hemispheres is 1 ' 53, and 

 the index ß of the astrophyllite is 1"733, we get from this: 



2V = 88° 10'. 



The axis of elasticity a being, as is otherwise the case, 

 perpendicular on the direction of cleavage, it becomes here the 

 acute bisectrix, and accordingly this astrophyllite, in contra- 

 distinction to what is generally the case, is optically negative. 



As before mentioned, the astrophyllite from Narsarsuk is 

 exclusively found as thin, flattened needles, sitting abundantly 

 on the other minerals, as for instance catapleiite, aegirite, el- 

 pidite, microcline, albite, epididymite, calcite, and rhodochrosite. 

 Often the astrophyllite sticks so loosely, that it may be removed 



