676 GREAT SERPENTINE BELT OF NEW SOUTH WALES, Hi., 



site(37). It has a very fine, confusedly fibrous structure, high 

 birefringence, often low by mutual compensation, and varying 

 green to brown pleochroism. A careful description of this 

 mineral was given by me, in a paper on some basic inclusions in 

 the Dundas volcanic pipe near Sydney(38). The suggestion there 

 was, that the mineral was produced by the action of atmospheric 

 agencies, as is usually the case. 



As pointed out by Professor Bonney (op. cit.), it is nearly 

 always possible to distinguish an antigorite-serpentine in the 

 field. It is peculiarly tough under the hammer, and breaks with 

 a rather rough, granular fracture. 



As antigorite-serpentine is frequently present in the Alpine 

 areas that have suffered the greatest pressure, a series of density- 

 determinations was made, to discover whether there was any 

 change in the passage from normal to antigoritic serpentine. 

 Five rocks were chosen, which, from their colour and micro- 

 scopical appearance, were considered to be the most nearly allied 

 in composition, and two carefully selected chips of each were used. 

 The results were as follows : — 



N. T. , 2 1 5 . Mesh serpentine and bastite rather 



deficient in magnetite 2*570 to 2-598 



N.T.,230. Mesh-serpentine and bastite ... 2-602 to 2-611 

 N.T.,240. Mesh-serpentine and bastite ... 2-612 to 2-615 

 N.T.,383. Antigorite-serpentine with bastite 2597 to 2-617 



N.T.,491. Antigorite-serpentine 2-620 to 2-632 



The difference in specific gravity, between an antigorite- and 

 a normal serpentine, is thus within the limit of variability of a 

 single specimen. Though the antigorite appears slightly the 

 higher, this may be due to the presence of magnetite, the specific 

 gravity of which is 3*1. It maybe concluded that the formation 

 of antigorite from mesh-serpentine is not accompanied by any 

 noteworthy change in density. The first serpentinisation is, of 

 course, associated with a decrease in density. The least altered 

 peridotite present, N.T., 212, has a mean specific gravity of 

 2-815, while a rather more serpentinised rock has a mean density 

 of 2-739. Fresh harzbergite varies, as a rule, from 3'17 to 3*35 

 in specific gravity (Rosenbusch). 



