negative. table vii. 
Structure. 
Association. 
Inclusions. 
Alterations. 
Occurrence . . 
Remarks. 
Usually in 
granular ag- 
gregates in 
cavities, in 
bands or veins. 
Also in irreg- 
ular grains & 
simple indi 
viduals be- 
tween the 
constituents. 
In nearly all 
rocks which 
bear augite, 
hornblende, 
biotite and 
plagioclase. 
Fluid in- 
clusions, 
very poor 
in mineral 
inclusions. 
None. 
Primary and sole 
component of 
limestone, etc. 
Not known cer- 
tainly from erup 
tives except as 
secondary pro- 
duct, particularly 
of bisilicates and 
mica. In crystal- 
line slates as both 
primary and 
secondary. 
Well character- 
ized by rhombo- 
hedral cleavage 
and twin-lamel- 
lation. When in 
small grains not 
easily determined 
Reliance must be 
pu t upon the sol- 
ubility and colors 
of polarization. 
As above. 
Without the 
polysynthetic 
lamellation. 
As above. 
With 
serpentine. 
With olivine and 
serpentine as pro- 
duct of alteration. 
Magnesite ^ and 
siderite only 
chemically dis- 
tinguishable from 
calcite. 
As above. 
As calcite. 
In concentric 
shells and radiat 
ing spheres in an- 
decite. etc., as 
product of alter’n 
Irregular 
grains coales- 
ced with the 
other constit- 
uents. 
With so- 
dalite micro- 
cline, horn- 
blende, and 
titanite. 
Poor, fre- 
quently 
colored 
green by 
particles 
of horn- 
blende. 
Fibrous transition 
into zeolites. 
Easily recognized 
macroscopically. 
solubility and Na 
reaction forming 
good characteris- 
tics. 
Primary essential 
component of 
older eruptives, in 
elaeolite-syenites. 
In crystals or 
aggregates of 
minute irregu- 
lar grains. 
Withleucite. 
augite, or 
with sani- 
dine and au- 
gite, or with 
hornblende 
and titanite. 
Frequent- 
ly augite- 
microlites 
arranged 
parallel to 
the sur- 
faces. 
Usually unaltered 
in phonolites or 
polarizing like an 
aggregate and 
cloudy, showing 
passage to zeolites 
Primary compo 
nent of later 
eruptives, nephe- 
linites, nepheline 
-and leucite-ba- 
salts, phonolites 
and teph rites. 
See below. 
P 
Fibrous, coa- 
lesced with 
nepheline and 
orthoclase. 
As in 
eiaeolite. 
Poor, iron 
oxide 
flakes, as 
in eiaeo- 
lite. 
Fibrous decompo- 
sition forming cal- 
cite. (Cancrinite 
seems to be but 
an alteration af- 
ter nepheline.) 
As eiaeolite, 
rare. 
Distinguished 
from eiaeolite 
only macroscop- 
ically by amt. of 
Ca CO3 
Only as fiag- 
ments in 
macroscopic 
crystals. 
With flesh 
colored orth- 
oclase and 
mica. 
Apparently only a 
total alteration of 
nephelin(?)'or cor- 
dierite(?), largely 
consists of minute 
muscovite scales. 
Rare in orthoclase 
porphyry. 
Easily recognized 
by crystal form | 
and alteration. 
Zeolites usually show their secondary character. Tridymite has no such short rectangu- 
lar longitudinal sections. When nepheline appears as an aggregate of minute grains it can 
be distinguished from colorless glass-masses or quartz or othoclase aggregates by micro- 
chemical methods. 
