410 JULIEN 



The lateral bands with cross fibration show high interference 

 colors and often a strong pleochroism, pale bluish green and 

 greenish yellow to orange, yellow or colorless. Extinction 

 parallel or normal to plane of veinlet. In places, some veinlets 

 are thicker, continuous and parallel, so as to produce an appar- 

 ent close lamination, with a micro-augen structure, through the 

 lenticular form of intervening grains of a colorless mineral. This 

 seems to mark, not a schistose structure of the rock, but an 

 eminent cleavage or parting of the parent mineral, probably the 

 orthopinacoid, ooPoo (lOo), of diallage. The material of these 

 veinlets maybe composite, a mixture of chrysotile and chlorite,^ 

 or consist of micro-chrysotile, or often wholly of a mineral of 

 somewhat higher birefringence to which the brilliant polarization 

 colors may be mainly due, micro-nemalite, the fibrous form of 

 brucite. Under sufficient magnifying power, the two minerals 

 chrysotile and nemalite, may be easily discriminated by the rela- 

 tive position of their axes of elasticity, C ^yi'^g parallel to the 

 direction of the fibers in chrysotile, and ^ in nemalite. This 

 cross-fibration, in such veinlets within serpentinous rocks, has 

 been hitherto assumed to characterize chrysotile alone. But 

 in this serpentinoid, at least, the incomplete alteration shown in 

 the veins which traverse the outcrop, enclosing brucite partly 

 altered to nemalite and the latter partly to chrysotile, also ex- 

 tends to the microscopic veinlets, which may comprise both 

 micro-nemalite and micro-chrysotile. The general relation of 

 these two minerals is the subject of another investigation. 



The interspaces in the knitted or bar structure rarely exceed 

 O.I or 0.2 mm. in length, usually predominating in volume of 

 the rock. In places, they are occupied largely by a colorless 

 substance, without relief, cleavage or texture, but which is not 

 isotropic or structureless, as it first appears under low power ; 

 or it may be greenish yellow and feebly pleochroic, greenish to 

 yellow. Between crossed nicols it offers an irregular aggregate 

 of blades and plates, with sometimes a very minute platy tex- 

 ture, fibrous in places. Low birefringence shown by feeble 

 interference colors, pale gray or bluish gray to bluish white of 



' Newland, loc. cit., 317. 



