159 
upon closer inspection they are seen to enclose poikilitically 
all the other constituents of the rock with the exception of the 
egirine. 
Microscopic characters. — Under the microscope the rock 
is seen to be made up of the following main constituents; 
felspar, nepheline, eudialyte, ægirine, and arfvedsonite. Anal- 
cime is present in very varying amount but this mineral is 
apparently always of secondary origin. Locally the rock con- 
tains large icositetrahedral phenocrysts of analcime which per- 
haps indicate the original presence of leucite(|?). Primary sodalite 
010 
Fig. 15. Microcline in lujavrite, Fig. 16. Albite in lujavrite, 
basic section (X 70). basic section (X 120). 
is not common. Minor accessories are often entirely absent; 
only in a few instances fluorite, sphalerite, biotite, and astro- 
phyllite have been observed. Besides analcime also catapleiite, 
sodalite, hydronephelite, and natrolite occur as secondary pro- 
ducts, 
The felspars of the ægirine-lujavrite are microcline and 
albite. The crystals are of tabular habit parallel to 6 (010) and 
slightly elongated parallel to the a-axis. The length averages 
3 or 4 millimeters (varying between 1 and 6 millimeters), and 
the mean thickness is about 0/4 millimeter (0'1—0'7 millimeter). 
The mode of crystallization of the alkali-felspars of this rock 
