360 MINERALS IN KIMBERLITE 



excluding those that have been formed by alteration 

 subsequently : 



(a) Tremolite, hornblende, epidote, orthite, tourmaline, 

 rutile, muscovite, biotite, apatite, and possibly zircon. 



These have evidently been derived from granite and 

 gneiss, actinolite-schist, and probably also from inclu- 

 sions in the granite. 



(6) Olivine, enstatite, chrome-diopside, garnet, brown 

 mica, occasionally ilmenite, magnetite and chromite, 

 more rarely hornblende, spinel, sphene, cyanite, sap- 

 phire, graphite and the diamond. 



These minerals have probably been derived from the 

 basic and ultrabasic holocrystalline (and sometimes 

 granulitic) rocks ; the most noticeable feature in this list 

 is the absence of perofskite and the very infrequent 

 occurrence of iron ores ; the diopside, too, is usually a 

 different variety to that included in (c). 



(c) Olivine, diopside, enstatite (?), brown mica, mag- 

 netite, ilmenite, apatite, perofskite, and meliJite (Matjes- 

 fontein, Sutherland). It seems that these minerals can 

 with a considerable degree of probability be ascribed to 

 an eruptive magma which solidified during its ascent in 

 the pipes and incorporated in its mass certain of the 

 minerals of the groups (a) and (b). This eruptive matter 

 is represented by certain brecciated fragments and occa- 

 sionally by narrow veins in the blue-ground ; in these 

 forms it is free of any foreign inclusions and shows 

 porphyritic crystals of olivine, diopside, mica, and pos- 

 sibly enstatite, set in a serpentinous ground mass crowded 

 with little crystals of perofskite, apatite and iron ores. 

 In some cases it is markedly vesicular. It is, therefore, 



