94 



on account of the pegmatitic vein on the top of the mountain 

 with gigantic individuals of feldspar and arfvedsonite ^). The 

 erikite, which is found on a very limited territory, is not, how- 

 ever, in near connection with any of these occurrences. 



The rock, in which the mineral is found, is nepheline- 

 syenite, viz. arfvedsonite-iujavrite with lenses of sodahte-syenite^). 



Crystalline form. 

 The erikite is rhombic with the axial ratio: 

 a:b :c = 0-575522 : 1 : 0-757961. 



The faces are generally not very well developed ; some- 

 times, to be sure, they may be rather bright; but even when 

 this is the case, they are most frequently more or less striated 

 or curved. As is seen from the table below, the angles, even 

 in the best faces, deviate V2 — 1° from each other, and in faces 

 of slighter value the deviations may increase to ca. 3°. Even 

 if the signals, seen in the goniometer, appear sharp and simple, 

 the angles found vary nevertheless from one measurement to 

 the other, probably owing to the presence of vicinal faces. For 

 fundamental angles have been chosen the angles of the two 

 principal zones showing the smallest mutual deviations, and it 

 will be seen that the values found and the calculated ones 

 upon the whole correspond tolerably well; it has been possible 

 to determine all the observed faces with small indices, so that 

 they may be regarded as completely sure. 



Steenstrupite. Medd. om Grønland XXIV, 1901, p. 205, and «Epistolite», 



a new mineral, ibid. p. 183. 

 ») G. Flink, I.e. 



N. V. Ussing: Mineralogisk-petrografiske Undersøgelser af Grønlandske 



Nefelinsyeniter. Medd. om Grønland XIV, p. 22 (The locality is here 



called Serrarsiut). 

 ^) With regard to the nomenclature of these rocks the reader is referred 



to the paper by N. V. Ussing quoted above (French resumé on 



p. 403). 



