180 ki.\ij!i:ki-itk i-ko-M uklgiax congo. 



of the triLutaries of tlie Lucliipuka River. Some time ag'o 

 lie received from. Mr. M. Poulsen a fine specimen of com- 

 paratively fresh kimberlite from the Msipashi pipe, situated 

 some miles to the north-east of the Kambeli pipe,* Avhich again 

 proved to be practically identical with the kimberlite from tlie 

 lower levels of the Kimberley pipe. 



It is a heav3' rock of blackish-g-reen colour, composed of 

 a dark serpentinous ground-mass, in wjiich are imbedded large 

 irregular grains of olivine and ilmenite, and rounded grains 

 of deep red pyrope bordered by dark kelyphite rinds, 

 the minerals named being accompanied by occasional grains 

 of enstatite and chrome-diopside and very occasional flakes of 

 phlogopite. Thin sections of the rock sIioav that olivine of at 

 least two ages is present. To the earlier of these belong the 

 megasopic grains, which are rounded or quite irregular in 

 form, some of them evidently having been derived from the 

 fragmentation of yet larger grains. It is probable that cognate 

 xenocrysts, as well as true phenocrysts, are represented 

 amongst them. They are all in an advanced state of 

 serpentinisation, and many of tliem have been completely 

 replaced by serpentine or by serpentine and calcite. The 

 smaller olivines, without exception, have been completely 

 replaced. Tlie serpentine is of yellowisli-green colour, and is 

 seen under high powers of magnification to be composed of 

 radial aggregates of minute scales and fibres having the optical 

 properties of (dirysotile. The serpentine, as already indicated, 

 is frequently accompanied by cahnte, the latter mineral having 

 clearly developed at the expense of the former. Many of the 

 smaller pseudomorplis exhibit a zonal structure, a core of 

 calcite being surrounded by an outer zone of serpentine. 



Large and small olivines together make up about 60 per 

 cent, of the rock. The ilmenite occurs for the most part in 

 irregular grains, but at the extremity of one grain crystal 

 faces were observed. Most of the grains, which are up to 

 9 millimetres ac^ross, are surrounded by narrow " reaction " 

 rims composed of small crystals of perowskite. 



The pyroi)e occurs in rounded grains up to 5 millimetres 

 across, encased in broad kelyphitic rinds. These exhibit a 

 zonal structure. At their inner periphery and in direct contact 

 with the pyrope, or separated from it by a narrow colourless 

 selvage, is a translucent zone of pale yellowish colour com- 

 posed of minute radially disposed fibres. The latter have a 

 high refractive index a-nd fairly high birefringence. They 

 extinguish obliquely at angles up to 44°, and would thus 

 appear to be composed of a mineral belonging to the family 

 of the monoclinic pyroxenes. The minute size of the fibres 

 renders their closer identification impossible. This zone is 

 succeeded outward by a broad opaque zone of deep reddish- 

 brown colour, that in turn merges into a narrow outer zone 

 composed mainly of lustrous particles of magnetite. In some 



* The situation of both pipe.s is sliown on the map pnlilislied on 

 p. 102 of •' The Diamond Fiekls of Soiithorn Africa." 



