PETROGRAPHY. 
show some crystal planes, or are subhedral. Twinning is common, but is not very 
marked, and in most specimens the phenocrysts of both feldspars are about equal 
in amount. Small, subhedral, often fragmentary phenocrysts of augite are rather 
more abundant, and are almost wholly colorless, only the larger ones showing a 
faint greenish tinge. The somewhat less numerous olivine phenocrysts are like- 
wise small and subhedral, most of them having the customary crystal planes. They 
are much less fractured than the augites and occasionally are euhedral. In thin 
section they are colorless, but often have a thin outer border of yellow or brown 
substance, which is probably iddingsite. 
The groundmass is typically holocrystalline and the fabric a felted one, due to 
the diverse arrangement of the feldspar laths. It is made up in great part of very 
small laths of feldspar, those of orthoclase more numerous than those of labrador- 
ite, with small prismoids of augite and grains of magnetite. These are scattered 
without definite arrangement, giving rise to the felted fabric, through a colorless 
cement, which usually shows somewhat faint birefringence and is referred to ortho- 
clase. In a few specimens this is replaced by a colorless glass, the amount of which 
is always negligible, and it is often a matter of difficulty to decide with finality on 
the holocrystalline character of such groundmasses. In rare cases, as in a flow 
south of Soriano, the feldspathic cement presents an ill-defined poikilitic texture, 
irregular and vaguely bounded areas extinguishing simultaneously. 
Chemical composition. Of fiescolal ciminose two analyses are available, both of 
which have been published previously. As given below they include recent deter- 
minations of P 2 O S and also a redetermination of TiO 2 in I, with proper corrections 
of the figures for A1 2 O 3 . It must be noted that the original analysis of this type* 
was incorrect as regards alumina and magnesia, as was pointed out in a later pub- 
lication,! and is therefore to be rejected and replaced by that given here. 
Chemical Composition of Fiescolal Ciminose [Ciminite]. 
I. 
II. 
I. 
II. 
SiO 2 
C(.,l6 O.O2.1 
C7. 71 O. O?? 
CO 2 . . 
none 
none 
A1 2 O 3 
Fe 2 O 3 
14.47 -142 
1 . 74. . OO8 
14.41 .141 
I . 2 I . Oo8 
TiO 2 . . . 
P,O<. .. 
0.53 0.007 
o. 76 .007 
0.40 0.005 
0.30 .002 
FeO 
4.50 .062 
A. 77 . o6l 
MnO . . . 
n.d. 
n.d. 
MgO 
PaO 
7.90 .198 
7.80 .195 
BaO.... 
none 
Na 2 
i . 79 . 029 
1-35 .022 
IO0.2I 
100. 61 
K 2 O 
H 2 O+ 
6.63 .071 
O. 27 ) 
6.38 .068 
Sp. gr. . . 
2. 70 at 10 
H 2 O- 
U.^ 1 
o. is S 
0.18 
I. Fiescolal ciminose [ciminite]. Fontana Fiescoli, Cimino Volcano, Ciminian District. 
Washington, analyst. Am. Jour. Sci., IX, 1900, p. 44. 
II. Fiescolal ciminose [ciminite]. La Colonetta, Cimino Volcano, Ciminian District. Wash- 
ington, analyst. Am. Jour. Sci., IX, 1900, p. 44. 
* Jour. GeoL, IV, 1896, p. 837. 
^Am. Jour. Sci., IX, 1900, p. 45- 
