Hornblende from Italy. — Van Horn. 373 
We therefore obtain the following proportions: i2H.jO: 
4Na.^0: j6CaO: 36MgO: 13AI2O3; SoSiOg: which written as 
a formula gives H.^^ (Na, K)g Ca^g (Mg, Fe)3g (Al, Fe).^^ 
^'50 ^207- Thison calculation gives the following per cents, 
for its theoretical composition: 
Calculated. Found. Difference. 
SiOg 42.099 42.162 +0-063 
AlgOg.iFeaOg) 18.607 18.604 — 0.003 
MgO, (FeO). 20.207 20.225 + 0.018 
CaO 12.573 12.527 —0.048 
NagO, (KoO) 3.480 3-509 -|- 0.029 
H3O 3-031 2.971 — 0.060 
99.997 99-998 
We see from the formula that this hornblende is ver}- 
near an orthosilicate, and that it is in reality slightly more 
basic than such a one. This is seen more clearly if we simp- 
lif}' still rnore the formula above given by calculating Fe.^Og 
as Al.^Og, FeO and CaO as MgO, Na., O and K.,0 as H.,d. 
We then obtain the following: 
1. II. III. IV. V. 
I on basis Molecular Simplifl- Molecular 
of loU. propor- cation proportions 
tions. of III. taken. 
SiOo 39-473 44-88i 748 3-85 4 
AI0O3, (FegOg).. 17.418 19.804 194 1. 00 I 
MgO, (FeO, CaO) 27.312 31.054 776 4.00 4 
HgO.lNaoO.KgO) 3.747 4.260 236 1.21 i 
87.950 99-999 
We have then H.,0: 4MgO: AL^O.,: 4SiO., or (H, K, 
Na).3 ( Mg, Fe, Ca)^ (Al, Fe)., Si40i6 from which is easily- 
seen that the proportions are those of an orthosilicate. If 
we calculate the theoretical composition of this formula we 
obtain as follows: 
Calculated. Found. Difference. 
SiO, 46.15 44.48 —1.27 
AL03,(Fe203).. . 19.61 19.80 +0-19 
MgO,(FeO,CaO). 30-76 31.05 +0.29 
HgO.iNa.O.K^Oj 3.46 4-26 +0.80 
99.98 99.99 
Since the differences are so very slight it seems best, and 
certainl)' much more simple, that we accept this abbreviated 
