The Parent-rock of the Diamond in South Africa. 



227 



Fig. 1. — Section of the diamond-bearing eclogite. Pyropes with, narrow kelyphite 

 borders, and chrome diopside intercrystallised. The clinopinacoidal cleavage 

 of latter risible in the lower part of the section. 



to decomposition, a form of the well known kelyphite rim, sometimes 

 a mica, sometimes a chlorite, possibly now and then associated with 

 a little minute hornblende. In a few cases a " rim " is brown in the 

 outer part and green within. The constituents tend to a parallel 

 rather than a radial grouping. The garnets occasionally contain 

 minute branching root-like enclosures grouped in bands. Though these 

 act on polarised light, I regard them as empty cavities, and attribute 

 this to diffraction. 



(b) Chrome-diopside. — The mineral described under that name by 

 Professor Lewis, and referred to by others as omphacite or sahlite. The 

 individuals are sometimes about a quarter of an inch long. In thin 

 slices it is a pale dullish green colour, inclining to olive ; under the 

 microscope, a pale sea-green, with a trace of pleochroism. It has one 

 strongly marked cleavage, not however nearly so close as in ordinary 

 diallage, and a second weaker, sometimes approximately at right 

 angles to it.* On examining flakes, obtained by crushing, I find the 

 strong cleavage to be clinopinacoidal and the other probably basal, 



* One may give a general idea of their relative importance by comparing them 

 to the columns and cross- joints in some basalts. 



