HORNBLENDE AND BYTOWNITE FROM HYPERSLTHENE GABBRO. DAG 
I. Chemical analysis of hornblende, Broken Hill. 
II. Calculated composition for hornblende with mean refractive 
index of 1:66. Amer. Jour. Sci, Vol. 37, 1914, pp. 183 
- 186. 
It will be noticed that the chief difference lies in the low 
percentage of ferric oxide and high percentage of ferrous 
oxide in the Broken Hill mineral. The axial angle also 
shows that the mineral is abnormal. 
[ELSPAR. 
(a) Chemical Composition. 
Since the felspar obtained by separation in heavy liquids 
was so clean, and the microscopic examination indicated 
that it was of constant chemical composition, it was con- 
‘sidered worthy of further investigation. An analysis, 
-earried out in duplicate, gave the following result :-— 





| IE if oyakle III. IV. 
| m0, P-CRO RE Speen AO Ou walle, | 42 
raved? O earn 1) 2062 322 old 
| Fe,O, avese  oaphol 5 
| FeO alass: | | 
CaO 1S 220 ss alosall 15:0 201 
MgO asctOSe 7 PaO om 
Na,O Whe 4 3a aa OH oa 39 
KO Cea a eke, 5 
H,O | 0-08 | 0:73 
| (100-31 | 100-49 100°1 
Sp. Gravity| 2:706* | 



# pi? 
I. Felspar from Gabbro, Black Blutf, near Broken Hill. 
lI. Felspar from Diahase, Skye. (Hintze, Handbuch der Min- 
eralogie II, (m) vxxvitl, p. 1528). 
III. Calculated Chemical Composition of AbgzAn;3. Iddings. 
ITV. Molecular Nos. for column I. 
