MINERALOGY OF BLACK LAKE AREA. 
41 
L (131) (f of Zambonini). First by Dana from Testa Ciarva; later by 
LaValle from Borne de Brous. 
Montreal chrome pit: Observed once on twin crystal as a very 
small face. 
* (121) Given in Goldschmidt's Winkeltabellen, but is not mentioned in 
Zambonini’s work on diopside. 
Montreal chrome pit : Observed on several crystals, one of them 
the twin crystal having the form L(131) as a small face. 
(552) Has been noted on green crystals of diopside from Rotenkopf, 
Zillertale. 
Montreal fhrorne pit : On one crystal as a line face truncating the 
edge (331:221). 
Chemical Composition . 
The material selected for analysis had a specific gravity of 3 * 267. 
The melt, after fusion, was coloured bluish-green, indicating the presence 
of manganese. The result of the analysis is given in column 1 below. 
Analyses of Diopside. 
1 
Montreal 
chrome pit 
(colourless) 
2 
Alatale 
(colourless) 
3 
Nordmark 
(limpid) 
(Flink’s type 
V) 
4 
Calumet 
island 
(white) 
5 
Near Ottawa 
(white) 
SiO s .. ......... 
54-77 
54*74 
54*59 
54*90 
54-50 
A1*0« 

.. 
Fe*Oi. 
0*17 
0*11 

FeO 
0-89 
2*91 
2-49 
1-98 
MnO . . 
0*11 
0-14 

MgO. ......... 
18*46 
17-02 
17-42 
16*76 
18-14 
Cat), . . . , .... 
26-33 
26*03 
25*70 
27-67 
25*87 
Volatile. ....... 
— 
— 
- — 
0*80 
0*40 
100-73 
100-70 
100*45 
100-13 
100-89 
2. Doelter, Tscherm. Mitth., 1877, 289. 
3. Flink, Groth's Zietschr., 11, 476. 
4. T. Sterry Hunt, Geol. of Canada, 1863, p. 468. 
5. Ibid., p. 467; white, semi-transparent, sp. gr. = 3-26— 3*27, from the vicinity 
of Ottawa. 
The diopside thus approaches very closely to the theoretical com- 
position, CaMg(SiOs) 2 j there is very little ferrous oxide present, replacing 
magnesia, and alumina appears to be entirely absent. It is possible 
that a slight error in the determination of the ferrous oxide is responsible 
for the small percentage of ferric oxide shown in the analysis. Diopside 
with this degree of freedom from iron (and alumina) is somewhat rare. 
The analyses of two other Canadian examples are given in columns 
4 and 5 above. In addition, columns 2 and 3 show the composition 
of colourless diopside from Alatale (Piedmont) and from Nordmark 
(Sweden), the latter representing Flink’s type V; these are included for 
