74 



appear especially in the end portions of the crystals and are 

 due to an alteration process to which the mineral is subject. 

 The combination of faces displayed by these crystals is shown 

 by Fig. 6, Plate IV. Here occurs the form м, which is very rare 

 on the primary aegirine ; its faces are brilliant, while the other 

 terminal faces are dull, as usual. 



Secondary aegirine occurs fairly widely distributed on 

 Narsarsuk. It is particularly abundant at the localities No. 2 

 and No. 5. The crystals are generally small and needle-shaped, 

 and less than 1"" in diameter. The thinner are translucent with 

 a green colour. Sometimes the individuals are hair-like , and 

 such crystals often form felt-like masses of greyish green colour. 

 Often the crystals occur in radiated groups implanted on larger, 

 primary aegirine crystals. They show a very simple combina- 

 tion of faces. In the vertical zone only the usual forms m, a, b 

 occur. The ends taper to a quadrilateral point, formed by 

 the forms x and or hke faces (Fig. 7, Plate IV). To the said 

 forms is added, especially on individuals of a somewhat larger 

 size, the form u, which may be said to be fairly characteristic 

 of the secondary ægirine in this place. On a few tolerably large 

 crystals belonging here the third pinacoid с has been observed 

 as a rarity. It is present as an extremely small triangular face, 

 and is briUiant like the faces belonging to the form и (Fig. 8, 

 Plate IV). 



As already mentioned, several aegirine crystals from the 

 locality No. 8 show yellowish brown zones and spots due to the 

 incipient alteration of the mineral. But in general the crystals 

 are , without exception , quite black by reflected light. Only 

 hair- like individuals and the thinnest splinters are translucent 

 with a green colour of different shades. Sections, too, must be 

 made very thin, in order that they may become translucent. 

 Such sections orientated parallel to the second pinacoid are trans- 

 lucent with a green colour inclining to yellowish brown. Under 

 the conoscope they show no axial image, the plane of the optic 



