8o 
THE ROMAN COMAGMATIC REGION. 
zonally arranged in thin bands parallel to the crystal outline. The great majority 
of the feldspar phenocrysts are of a labradorite, about AbjAn 2 , in euhedral, stout 
prisms, always twinned according to the usual laws. Phenocrysts of alkali-feldspar 
are less numerous, are somewhat less apt to be euhedral, and show Carlsbad twin- 
ning. The phenocrysts of augite of the usual pale-gray color are very rare, euhedral 
to subhedral, but often in fragments. 
The groundmass in which these lie is extremely fine-grained. It is composed 
in large part of minute feldspar laths, which are of both orthoclase and soda-lime 
feldspar, though their small dimensions and absence of twinning render exact 
determination difficult. With them are many small prisms and grains of colorless 
augite, small anhedra of olivine, and some magnetites. Between these lies a color- 
less cement, which is in part doubly refracting, and may be considered to be feldspar, 
since nephelite is absent, judging from tests on the rock powder. In places this 
interstitial substance is isotropic, these areas being usually round and probably of 
leucite, though their very small size renders identification difficult. Glass may also 
be present to a small extent, but could not be definitely established. 
Chemical composition. But one analysis was made of this type, hitherto 
unpublished : 
Chemical Composition of Foglianal Ciminose-auruncose [Leuctie-tephrite]. 
I. 
I. 
SiOj 
C2 . 37 O 
8?T 
H 2 O 
O. si 
A1 2 O 3 
20.89 
204 
CO 2 
none 
Fe 2 O 3 
1 . 21 
008 
TiO 2 
i. is 
0.014 
FeO 
A. AA 
062 
ZrO 2 
o. 07 
MgO . . 
I 74. 
O44. 
P 2 Or .. 
O ?! 
. 004, 
CaO 
t;.o8 
OQI 
SO, . . 
none 
Na 2 O 
2 .OO 
O47 
MnO 
n.d 
K 2 O 
7. 4.7 
O8o 
BaO 
o. 16 
H 2 O + 
99.96 
Foglianal ciminose-auruncose [leucite -tephrite]. Croce di San Martino, Monte Vico, Ciminian 
District. H. S. Washington, analyst. 
Or 
. . 44 . 48 "* 
| 
Ab 
. . 13 .62 
70 . S I 
An 
. . 21 . 41 
Ne 
. ^ . O4 
c .04 
Ol 
. 7 16 
7.l6 
Mt 
i . 86 
7 . QO 
11 
. 2.13 
I 34 
Ap 
. 1 . 34 
85-45 
12. 49 
97-94 
H 2 O, etc 2.20 
100. 14 
Class. 
Order 
Rang 
Subrang . 
Sal 
'Fern 
F 
'L 
K 2 O'+Na 2 O 
CaO' 
K 2 O' 
'Na,O' 
= 6.84 
I3-38 
1.65 
1.70 
