412 JULIEN 



Anomalies in their optical characteristics are partly due to 

 the fine fibrous aggregation and to phenomena of strain, but 

 doubtless in part to a slight but general intermixture with amor- 

 phous serpentine, shown in ordinary light by yellow streaks, and 

 perhaps with brucite. 



Within the interspaces of the network and imbedded in ser- 

 pentine, another mineral, colorless to grayish, with some relief 

 often occurs in irregular grains, elongated or lenticular, up to 

 0.3—0.5 mm. in length, by o. i mm. in thickness. They are 

 rarely massive, but finely granular or mylonitic, as by crushing, 

 though more or less indistinct parting planes, perhaps cleavage 

 traces, occasionally appear, even to a platy structure ; these make 

 an angle of 80° to S8° with the parallel serpentine veinlets. 

 Extinction generally wavy, as indeed with all the anisotropic 

 minerals, and imperfect ; maximum about 42°, though in some 

 cases parallel to cleavage. No interference figure in convergent 

 light was obtained. These grains may be assigned to an origi- 

 nal mineral constituent of the rock before serpentinization, prob- 

 ably disintegrated diallage, and now make up but a fraction of 

 one per cent, of the volume. 



Magnetite is also dispersed in considerable quantity through 

 both diallage and serpentine in these interspaces, in the form of 

 black dust, minute cubes and elongated aggregates, which may 

 reach 0.02—0.06 mm. These are largely gathered along the 

 walls of the interspaces or darken the sides of the partly altered 

 granules of pyroxene. 



A very few black particles consist of opaque, rhombic or 

 hexagonal plates, or translucent reddish, orange and yellow 

 scales, referred to hematite. 



The lattice structure is less common than the bar structure 

 and usually inconspicuous, presenting cells or interspaces 0.2— 

 0.3 mm, across. Within these, grains of amphibole occur in 

 two varieties. 



The one, considered to be remnants of a mineral antecedent 

 to serpentinization, occurs in colorless, broad fibrous sheets and 

 irregular grains, contrasting with the serpentine reticulation by 

 their good relief. They are granular, as by crushing, and rarely 



