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XXI. Enstatite Rock from South Africa, 

 By N. S. Maskelyne, F.R.S* 



MR. MASKELYNE exhibited sections of a rock from two 

 different localities in the Transvaal, which, when exa- 

 mined under the microscope, presented all the characters of a 

 very crystalline enstatite without affording evidence of the ad- 

 mixture of other minerals ; and this anticipation of its nature has 

 been subsequently confirmed by Dr. Prevost in Mr. Maske- 

 lyne's laboratory at Oxford. The specimens from which the 

 sections were made were collected by Mr. Dunn, who described 

 the two rocks in question as forming hills of boss-like form at 

 Korn Kopje, and at a place twelve miles south of Holfontein in 

 the Witfontein Mountains, to the south of Lydenburg in the 

 Transvaal. 



The occurrence of a pure and massive enstatite rock is new 

 to petrology, though rocks (such as lherzolite) are known in 

 which enstatite is a very prominent ingredient mineral. Its 

 occurrence in South Africa has, moreover, a special interest, 

 since Mr. Maskelyne first asserted the enstatitic or bronzitic 

 origin of the rock in which the diamonds occur in that region 

 of the world. The serpen iinized mass of which the diamond- 

 mines are composed was first shown, on crystallographic and 

 microscopic grounds, to have contained, and in no inconsider- 

 able degree to have consisted of, bronzite (ferro-magnesian 

 enstatite) ; and this was confirmed by actual analysis, by Dr. 

 Flight, of the grains of bronzite still left unaltered in that 

 rock. (See Quart. Journ. Geol. Soc. vol. xxx. p. 406, 1874.) 

 The diamantiferous rock, however, contains other minerals, 

 and must have been not very dissimilar to lherzolite. The en- 

 statite rock from the neighbourhood of Lydenburg is, on the 

 other hand, composed nearly exclusively of that mineral, which 

 is chiefly familiar to the mineralogist from its being an im- 

 portant ingredient of meteorites, and is likely, in other respects, 

 to become recognized as a more frequent ingredient of rocks 

 than has hitherto been anticipated, though, like the kindred 

 mineral olivine, the more ferruginous kinds have frequently 

 undergone a more or less complete serpentinization. The 

 Baste rock in the Hartz and the so-called pseudophite of Zdjar 

 are known to be still rich in enstatitic mineral, though other- 

 wise almost completely metamorphosed ; and in many serpen- 

 tines, such as that of the Lizard, crystals whole or in part still 

 survive as witnesses to the original nature of the rock. Mr. 

 T. Davies has also pointed out to the author of this notice that 

 the eulysite from Tunaberg presents, under the microscope, 

 the characteristic features of enstatite or bronzite in one of its 

 * Communicated by the Crystallological Society. 



