MINERALOGY OF BLACK LAKE AREA. 
51 
by hydrous ferric oxide. Some serpentine is also present in the section, 
being, no doubt, a portion of the dyke wall. 
Crystal Forms. The forms observed on the garnet crystals from the 
various pits, as far as they were examined, are as follows: 
Form 
Locality 
Colour 
Cube. ». a(100) 
Dodecahedron c!(110) 
Four-faced cube .......... £(610) 
8 * 8 e(210) 
“ * * .............. ...g(320) 
Three-faced octahedron r(332) 
Trapezohedron. m(311) 
* ... .............. o (2 11) 
Six-faced octahedron. .......... u(853) 
* 8 ........... .s(321) 
American chrome pit 
On all crystals 
Southwark pit 
American chrome pit 
American chrome pit 
American chrome pit 
Southwark pit 
On all crystals 
Union pit 
American chrome pit 
Amber 
Colourless 
Amber 
Amber; Union pit, rose 
Amber 
Colourless 
Rose 
Amber 
CHRYSOLITE. ' 
Chrysolite, or olivine, occurs only as a constituent of the peridotite 
and pyroxenite, and is described in the section dealing with these rocks. 
VESUVIANITE. 
Very finely crystallized specimens of vesuvianite are found at several 
localities in the area. The crystals have a brilliant lustre, are for the 
most part quite transparent, and display a wide range of colour, including 
pink or lilac, emerald-green, various shades of yellow, clove, and reddish- 
brown, and in some cases they are colourless; with the exception of the 
brown variety the crystals seldom exceed one millimetre in diameter. 
* 
Occurrences. 
Montreal Chrome Pit. This locality (Plates VI and VII and Figure 
16) has furnished some of the best material examined by the writers, 
lilac, emerald-green, yellow, and colourless varieties all occurring in 
fair abundance. 
The lilac vesuvianite forms compact, fine-grained, crystalline 
masses, having a deep tint which renders the specimens very striking 
and pleasing to the eye; it has been found that the colour fades somewhat 
after exposure to air and light. Examination of thin sections shows that 
the rock does not always possess the same structure. The vesuvianite 
has the usual high index of refraction and very low birefringence. If the 
section is somewhat thick, a faint, but quite distinct pleochroism is 
noticeable, the crystals appearing colourless for light vibrating in the 
direction of the prism edge, and pale lilac for light vibrating normal 
thereto. 
