440 V. F. MARSTEPvS— ASBESTOS DEPOSITS OF BELVIDERE MOUNTAIN 



regarded as having been derived from some form of basic eruptive. The 

 interpretation rests on the possible preservation and recognition of rem- 

 nants of mineral constituents belonging to the original mass, or in cases 

 of complete alteration, at least, the retention of some of the characteristic 

 and determinative structures belonging to the essential minerals of the 

 original rock. 



MICRO-STRUCTURE OF BELVIDERE SERPENTINE 



Types. — On the above basis the following types of structure have been 

 established as proof of the kind of rock from which the serpentine was 

 derived : 



(1) Mesh structure, in serpentine derived from olivine. 



(2) Bastite structure, in serpentine derived from enstatite or bronzite. 



(3) Lattice structure, in serpentine derived from non-aluminous horn- 

 blende. 



(4) Knitted structure, in serpentine derived from non-aluminous augite. 

 In the Belvidere serpentine, however, serpentization is so far advanced 



that the recognition of original structures belonging to minerals of the 

 original rock is rendered well-nigh impossible in the majority of cases. 

 There are, however, a few sections which shed some light on this most 

 interesting question. 



In sections of the normal and fine grained serpentine two distinct 

 types of micro-structure can be seen — one, a very complete fibration of 

 the rock, the other assuming a noticeable lamellar phase or possibly 

 scaly habit. If structure alone is the only essential element necessary 

 upon which to recognize and classify serpentines, the latter should be 

 regarded as lamellar or antigorite serpentine. 



Fibrous serpentine. — In the fibrous group at least two distinct arrange- 

 ments of the fibers may be seen, with all gradations between ; in one 

 the fibers are arranged in parallel series and in bundles ; in the other they 

 show a marked tendency to diverge at the ends or to radiate from centers, 

 and sometimes even to interlace. More than one phase may appear in 

 a single section. According to the interpretations of A. Lacroix and 

 others, the variations in structure may be and are used as a legitimate 

 basis for the establishment of distinct mineral varieties. If these va- 

 rietal forms, however, are crystallographically and chemically one and 

 the same thing, it would seem to be undesirable to give specific names 

 because of variation in form alone. 



The greater part of the Belvidere area shows a markedly fibrous struct- 

 ure. No particular arrangement is characteristic of any limited part of 

 the area. Coarse and fine textures may be found in the same prospect. 



