PETROGRAPHY. 
67 
II. 5. 2. 2. Bagnoreal Ciminose [Leucite-Trachyte, Bagnorea Type]. 
Megascopic characters. Rocks of this type are light gray in color, and while 
porphyritic are not strikingly so, as the phenocrysts are neither numerous, large, 
nor conspicuous. Those of leucite are most abundant, but constitute only from 5 
to 10 per cent of the rock. They are from i to 5 mm. in diameter and usually 
anhedral to subhedral, crystal planes not being well developed. There are a few 
very small black prismoids of augite, with an occasional biotite table. The ground- 
mass is rather light gray and quite aphanitic. 
Microscopic characters. In thin section the leucite phenocrysts show the usual 
characters, though the birefringence is weaker than in most cases and inclusions 
are rare. The phenocrysts of augite are subhedral, stout prisms, often fragmen- 
tary, and are of a somewhat greener tint than usual, though not markedly so. The 
biotite tables are brown, and for the most part are much altered to the common 
granular aggregate. Phenocrysts of feldspar are visible in the thin section, which 
escape observation in the hand specimen. They are of both orthoclase and plagio- 
clase, the latter a labradorite of about A^An^ Around these phenocrysts mantles 
of later alkali feldspar, oriented like the nuclear crystal, are not uncommon. 
The groundmass is typically holocrystalline and shows an intersertal fabric. 
It is composed in large part of feldspar prisms, most of these being of orthoclase 
with fewer of labradorite, the arrangement being diverse, with the other ground- 
mass constituents between the laths. Small round leucites are quite abundant, 
carrying few inclusions, and there are present in considerable amount small color- 
less augites, both in the form of subhedral prismoids and as anhedral, equant grains. 
Small grains of olivine are rather rare and the usual magnetite grains and apatite 
needles are seen. In some specimens there is a residual base of nephelite, intersti- 
tial between the other constituents, but this is not always found and its amount is 
very small in any case. 
Chemical composition. Incomplete analyses were made of two specimens of this 
type some years ago and are here republished, with several additional determinations. 
Chemical Composition of Bagnoreal Ciminose [Leucite-trachyte]. 
I. 
II. 
I. 
II. 
SiO 2 
??.8? O.Qtl 
cc.21 O.Q2O 
TiOj. 
O.?Q 0.007 
0.71 0.009 
A1 2 O 3 
18.34 .180 
18.78 .184 
ZrO a . 
none 
0. IO 
Fe 2 O 3 
2.77 .024. 
2 .60 OI7 
P-Oc. 
0.38 .003 
0.22 .OO2 
FeO 
i . 88 . 026 
2 86 . 040 
SO 3 .. 
o.os 
none 
MgO .. 
1. 73 .O4.3 
i . 68 . 042 
MnO 
n.d. 
n.d. 
CaO 
38-1 060 
4 6 i 082 
BaO 
0. 17 
0.18 
"Mn r\ 
K 2 O 
3-39 - SS 
8.77 .094 
3-13 - 5 
8.45 .090 
99.90 
99.61 
H 2 O 
CO a 
1.14 
none 
0.99 
none 
Sp. gr... 
2.648 at 27 
2.609 at 10 
I. Bagnorea] ciminose [leucite-trachyte]. Bagnorea, Vulsinian District. H. S. Washington, 
analyst. Jour. Geol., V, 1897, p. 370. 
II. Bagnoreal ciminose [leucite-trachyte]. Monte Venere, Ciminian District. H. S. Washington, 
analyst. Jour. Geol., IV, 1896, p. 849. 
