MINERALOGY OF BLACK LAKE AREA. 
79 
also different from that typical of hornblende asbestos. The latter either 
occurs associated with, and often completely coating other minerals, 
such as epidote, in which case the fibres have no regular arrangement; 
or it may occur in veins and fissures, where the fibres are invariably 
elongated in the plane of the fissure. (This does not apply to crocidolite 
which, of course, is distinct from ordinary hornblende asbestos, and 
usually has a deep blue colour.) 
The chryso tile-asbestos, on the other hand, in its typical mode of 
occurrence, forms veins in which the fibres, all packed parallel to one 
another, stretch transversely across from wall to wall of massive serpentine. 
The veins range in width from a mere fraction of an inch or less) 
up to 4 or 5 inches, and rarely even more, the majority of them being 
less than half an inch across. Chrysotile occurring in this way is known 
as “vein fibre" or “cross fibre,” and almost the entire output of the 
Black Lake-Thetford mines is of this type. 
Sometimes, however, the chrysotile lies along slip planes in the 
massive serpentine, and then the fibres, instead of being transverse, lie 
lengthwise in the fissure; such chrysotile, termed “slip fibre,” is, as a 
rule, not of such good quality as the cross fibre, being less flexible and 
harsher. Owing to the manner of occurrence, these fibres may appear 
to have a very considerable length, but this is due to the overlapping 
of a number of short fibres which are all matted together, more or less 
in parallel position, and in reality the slip fibre is usually shorter than the 
average cross fibre. This type is not so common in the Black Lake area 
as it is farther northeast, in East Broughton, where it forms the principal 
product mined. 
The analysis given on page 76 in column 3 shows the composition 
of the chrysotile; this analysis was made by M. F. Connor, and is 
reproduced from Dresser's report. 
Picrolite . 
The slip fibre just referred to has frequently been described under 
the name picrolite; the latter term, however, is more properly restricted 
to those fibrous, or columnar, varieties of serpentine, in which the fibres 
are difficultly separable and not very flexible, breaking with a splintery 
fracture. True picrolite, as thus defined, is not at all uncommon. It 
passes over into a rather massive, lamellar variety which might be classed 
as antigorite; this, however, does not separate into folia, but splits only 
along certain parallel zones of parting whose surfaces are often highly 
slickensided. This variety usually has an olive-green to bluish-green 
colour, and the same specific gravity and hardness as ordinary massive 
serpentine. 
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