26 
MUSEUM BULLETIN NO. 4. 
The thin section contains symmetrical sections of analcite 
phenocrvsts up to 4 mm. in diameter, mostly between 2 and 3 
mm., and some as small as 0*5 mm. Cubic cleavage is highly 
developed. These phenocrysts are evidently slightly altered, 
and now show rounded and polygonal light buff areas surround- 
ed by varying sized veins and patches of lighter coloured analcite, 
the arrangement giving a variegated appearance to the mineral. 
The deeper buff patches are faintly but distinctly doubly refract- 
ing, and the veining is arranged in rectangular directions, sug- 
gesting slight alteration (perhaps recrystallization) governed by 
cleavage directions. Bordering parts of some phenocrysts is 
a distinct rim up to 0 05 mm, wide of clear, faintly doubly re- 
fracting analcite. This rim is in some cases fastened directly to 
the phenocrysts, in other places being separated by a film of 
groundmass material; occasionally minerals of the groundmass 
project into the rim, so its outer boundary is in part gradational. 
This rim probably represents the groundmass stage of crystalliza- 
tion, during which analcite from the groundmass was added to 
that already in phenocryst form. 
The buff colour of the analcite is due to numerous very 
minute, dust-like inclusions, which are less numerous In the 
lighter veining and do not appear in the clear analcite rims. 
Some of the phenocrysts are broken, and the fragments dis- 
placed by groundmass material. 
Besides the analcite, subordinate phenocrysts of aegirite- 
augite, orthoclase, titanite, and melanite are found. 
^Egirite-augite occurs as idiomorphic tabular forms up to 
1 mm. long, twinned in some cases, and quite fresh. It resembles 
segirite-augites previously described. 
Orthoclase is found sparingly as tabular crystals up to 0 • 6 mm. 
long. They show Carlsbad twinning, and are clear and unalter- 
ed. Along the sides, for a distance of 0*03 mm. inside the 
crystal are microlites of augite and apatite( ?) orientated parallel 
to the sides of the crystal. They give the appearance of suc- 
cessive stages in crystal growth, and are probably analogous to 
the rims on the analcite phenocrysts. 
The melanite phenocrysts are about 0 * 3 mm. in diameter, 
and are similar to the other occurrences of the mineral, exhibiting 
irregular cleavage, zonal banding, etc. 
