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large masses : they shade off into felspathic rocks, becoming 

 enstatite — olivine — gabbro — olivine — norite, and even among 

 themselves they appear to be subject to much local variation 

 in one and the same mountain mass. It is unusual to find 

 them in such a fresh condition as on the Arthur River. 

 The saxonite of the Red Hill, West Coast, New Zealand, 

 containing the nickel-iron alloy awaruite * is said to be 

 the only other occurrence in the world where the rock is 

 fresh or nearly so: generally it is strongly serpentinised. 

 Oliviue — enstatite rocks have been described from the Straits 

 of Magellan, Borneo, Oregon (nickeliferous), Greenland, 

 Finland, Norway, United States, and the Hartz. 



Macroscopical Structure. — This is a characteristically heavy, 

 somewhat dull and dark-coloured rock, in which the brown, 

 waxy olivine is the predominating feature : occasional and 

 fairiy distinct plates of the rhombic pyroxene may be 

 detected, but to the eye they do not appear to be by any 

 means abundant. It occurs as a dyke of limited extent at 

 the upper Arthur River (W. R. Bell). The structure is 

 hypidiomorphic granular. Rosenbusch calls a structure 

 granular, in which only one generation of the constituents 

 exists, no recurrence of phase having taken place, and 

 hypidiomorphic when mostly allotriomorphic and partly 

 crystalline forms prevail. 



Microscopical Appearance. — Olivine forms nearly one-half of 

 the rock. In transmitted light this mineral is colourless 

 and remarkably fresh in appearance. Still it is traversed 

 by fissures, sometimes darkened with the deposition of some 

 iron oxide, or filled with yellow serpentine. The olivine 

 grains are sometimes rounded, but often show a marked 

 disposition to form idiomorphic crystals. 



Enstatite is generally in somewhat larger forms than the 

 olivine ; is colourless and non-pleochroic in thin sections, 

 but where the section is thicker, it is faint yellow and feebly 

 pleochroic. As a rule its cleavage cracks serve to distinguish 

 it from the olivine, and in the larger crystals the forms are 

 less perfect than those of the other mineral. It encloses 

 small intergrowths of a monoclinic pyroxene. It is in a 

 fresh condition while the olivine is frequently meshed with 

 serpentine, and sometimes wholly replaced by it. 



Magnetite is not so prevalent in peridotites as chromite or 

 picotite, but we see no translucent forms, and hence refer 

 the scattered rounded quadrate and other opaque grains 

 to magnetite. At any rate we see none of that translucency 

 at the edges which would indicate chromite or picotite. 



* On the discovery, etc., of Awaruite on the West Coast of the South Island 

 of N.Z., by Prof. G. H. F. Ulrich. Q. J. G. Soc, Nov., 1890, p. 619, 632. 



