106 



21. Analcime. 



The only zeolites met with on Narsarsuk are analcime and 

 natrolite. They were found closely associated at the locality 

 No. 2, both in small quantities. Besides calcite and rhodo- 

 chrosite, they are the last-formed minerals at this locality. The 

 minerals of the immediately preceding generation , on which 

 these four minerals are implanted, are microcline and aegirine. 

 The microcline is, as usually, coated with crystals of albite 

 in parallel orientation. The albite crystals are partly of the usual 

 habit, i. e. tabular parallel to the second pinacoid, and partly 

 prismatic or needle-shaped parallel to the c-axis, being analogous 

 to the albite crystals from Lille Aröe near Langesund previously 

 described by the author ^). The calcite, which seems to be the 

 oldest of the four latest formed minerals, consists partly of small 

 crystals bounded by the faces of the fundamental rhombohedron, 

 and partly of spathic masses forming the immediate substratum 

 to which the analcime crystals are attached. 



The largest analcime crystals attain about l""' in diameter. 

 They are closely aggregated into druses and crusts, so that on 

 each individual only a few faces have been developed. On these 

 crystals the common icositetrahedron n = (21 1} is the only 

 form that has been observed. The freely developed faces are 

 smooth and brilliant. The colour generally is enamel-white, but 

 not infrequently the mineral presents a bluish tinge. When 

 it could not assume a regular crystal form, it often has a 

 yellowish colour. 



The optical anomalies of analcime from other locahties are 

 also exhibited by the analcime from Narsarsuk. Fig. 2, Plate Vi gives 

 a somewhat diagrammatic representation of a section orientated 

 parallel to a cubic face, as it appears under the microscope. 

 It is divided by irregular lines into eight fields, of which every 

 two opposite ones have the same optical orientation. Each field 



Bull, of the Geol. Inst, of Upsala, Vol. IV. 1898, p. 23. 



