150 
Minute prisms of æginine and of arfvedsonite are always 
found included in the felspar of the naujaite. They are, however, 
neither so numerous nor so small as in the sodalite of this 
rock. Another difference is that, among inclusions in the 
felspar, ægirine is predominant, while, in the sodalite, arfved- 
sonite-prisms prevail. The commonest alteration of the felspar 
in this rock results in the formation of analcime. 
The felspar of the naujaite has often been partially con- 
verted into analcime. Among the slices of one single hand- 
specimen some may afford marked instances of this conversion 
while in others the felspar is quite intact. The transformation 
always begins from the margin and from a few cracks, and the 
analcime formed in this way is very coarsely crystalline, showing 
distinct cleavage and the usual anomalous double refraction. 
Curiously enough in many cases only the microcline has been 
altered to analcime while the albite is unaltered: instances of 
the reverse, however, are not uncommon. 
The principal dark-coloured minerals of the naujaite are 
œægirine and arfvedsonite. The former is predominant in some 
places and the latter in others, but these variations are quite 
irregular and specimens containing ægirine and arfvedsonite in 
about equal amounts are also rather commonly found. Both 
minerals occur as large allotriomorphic anhedra often reaching 
a length of 20 or 30 centimeters. Each anhedron encloses a 
large number of sodalite-crystals poikilitically (sometimes several 
hundred). Upon closer inspection egirine proves a little more 
idiomorphic than the arfvedsonite: while the latter is always 
interstitial and never shows any trace of external crystal faces 
geneous mixed crystals; while the primary perthitic felspars found in 
the Ilimausak pegmatites, in the naujaite, and in many other rocks, 
have crystallized at a lower temperature than the inversion temperature 
at which the felspars are transformed into non-isomorphous forms. 
The latter view of course depends on the assumption which has not yet 
been strictly proved, that the alkali-felspars are isomorphous at high 
temperatures. 
