372 The AmericMi Geologist. Juno, i893 
I. II. III. IV. 
SiOg 39.58 3Q.Q2 39.80 3917 
TiOg Trace 
AI3O3 14-91 14.10 14.28 14-37 
fCgO, 4.01 6.00 2.56 12.42 
FeO 10.67 11-03 19.02 5.86 
MnO Trace 0.30 1.5 1 
Mgo i3-o6 10.72 g.io 10.52 
CaO 11.76 12.62 10.73 II. 18 
Na^O 2.87 0.55 1.79 2.48 
KoO 0.62 3.37 2.85 2.01 
H2O 2.79 0.37 1.42 0.39 
100.27 98.98 101.55 99.91 
Sp. G. ...3.217-3.222 3.282 3.298 3.33 
In the anal)'sis the direct determination of water is given. 
Water as ignition was 1.29. The first glance at the analysis 
shows us that our hornblende is a very basic one with a high 
percentage of alumina and an amount of alkalies which is 
quite rare for hornblendes occurring in gabbroid-noritic 
rocks. In the Jan Ma)'en mineral ferric iron predominates, 
while the Pavone hornblende has mostl}' ferrous iron. The 
hornblende analysis most nearly resembling ours is the one 
from Mt, Vesuvius given under II. It is certain that in the 
analysis of many hornblendes, not enough attention has been 
paid to the determination of the water which, I think, plays 
an important role in the composition of the more basic mem- 
bers of this famih'. Many determine this only by ignition 
which always gives too low a result, as part of the oxygen 
is used for the oxidation of the ferrous iron. The direct de- 
termination according to the Sipocz-Ludwig method is apt 
to give a result somewhat high. However, in my analysis a 
large number of "blind trials" were made before the analysis 
itself was carried out and the percentage of water here is, I 
think, very little, if any, higher than it should be. If we 
compute Fe.^ O3 as Al^ O3, FeO as MgO, and K.^O as NagO, 
we can make the following calculation of our analysis: 
I. II. III. IV. V. ' VI. 
I ou Molecular Sinipli- Molecu- Propor- 
ba.sisof propor- ficatiou lar i)ropor- tioii.s 
lot). tions. of III. tion.s taken, in whole 
numbers. 
SiOg 39-473 42.162 700 12.50 12.50 50 
AlsOg.iP'eaOg) 17.418 18.604 182 3.25 3.25 13 
MgO, (FeO). . 18.935 20.225 505 9.01 9.00 36 
CaO 11.728 12.527 223 3.98 4.00 16 
Na^O, (KgO).. 3.285 3-509 56 1. 00 1. 00 4 
HgO 2.782 2.971 165 2.94 3.00 12 
93.621 99-998 
