MINERALOGY OF BLACK LAKE AREA. 
69 
ally the same composition as the crystals. The approximate composition 
of the matrix, as calculated from the analysis, would be near 6Mg0.AI 2 03. 
3Si08.7H 2 0; if it is composed in part of colerainite of composition 
4 MgO.Al 2 O 3 . 2 SiO 2 . 5 H 2 O, it is necessary to assume the presence also of 
some admixed hydrous magnesian silicate, near serpentine. 
Colerainite may be regarded as a basic orthosilicate, with the 
constitutional formula shown below; it maybe compared with newtonite 1 
from which it differs in having the two monovalent radicles (MgOH)s 
in place of two hydrogen atoms. 
Si04EEEEE-(Mg0H) 8 .H 
/ 
AI— OH 
\ 
OH 
Colerainite 
SiQ, = H,, 
/ 
AI— OH 
\ 
OH 
Newtonite 
When heated at first gently to dehydration, and then strongly 
in the blowpipe flame, the mineral whitens, disintegrates, and falls to 
pieces, showing a tendency to exfoliate, and finally it fuses with little 
or no intumescence to a white, rather lustreless, glass. Moistened with 
cobalt nitrate and heated, the mass becomes blue. Heated in a closed 
tube, the mineral whitens, decrepitates, and flies to pieces, and at a high 
temperature gives off much water. It is decomposed with difficulty 
by hydrochloric acid with separation of flocculent silica, but apparently 
without going entirely into solution. 
The behaviour of the compact matrix is similar, with the exception 
that it does not fall to pieces to the same extent on heating, and as a 
consequence it appears to fuse more easily. 
In some specimens, the crystals are in part covered with a later 
deposit of a cream coloured amorphous substance, which has the lustre 
and rather the appearance of polished meerschaum. In one specimen 
collected, two nearly adjacent druses, which are lined with crystals of 
colerainite, are partly filled with this material, the flat surfaces of the 
deposits in the two druses being parallel to one another. This material 
was not analysed. It has a hardness rather below 3, and the specific 
gravity is 2-45. Thin splinters fuse quietly in the bunsen flame to a 
white opaque globule, and the substance becomes pink when moistened 
with cobalt nitrate and heated. 
Colerainite was observed at only one other locality in the area, 
specimens having been collected on a dump near the Union pit, from which 
they doubtless came. The specimens have the same botryoidal form as 
those from the old Standard mine described above, but they are not 
nearly as well crystallized. The botryoidal spheres vary in diameter 
1 Clarke, F. W., "The constitution of the natural silicates;" U. S. Geol. Surv., Bull. No. 588, 1914, 
p* 83. 
