I9I5- No. 4- 



REPORT ON ROCK-SPECIMENS. 



21 



Amphibolite. The specimens are fine-grained, dark-coloured rocks 

 with high spec, gravity; the size of the constituent mineral grains is about 

 1.5 — 2 mm. They consist of the following, seen with the naked eye: 

 magnetite, pyrite, dark amphibole, black biotitç, plagioclase, white in colour 

 and showing twinningstriation on the cleavageplanes and finally a few 

 grains of quartz. The structure seems to be that of an igneous rock with 

 no prominent signs of squeezing. One specimen shows a small intruded 

 granite-vein with segregation of biotite on both sides. 



Fig. 10. Amphibolite (anal3'sedi. Scott's Nunataks. Micro-photo. Pol. light. Enlarg. 17. 



The microscopic examination has given the following results: 



The chief constituents of the amphibolites are basic plagioclase (labra- 

 dorite to bytownite), amphibole and biotite. The contents of quartz are 

 variable. Pyroxen and epidote are very rare. (Fig. 10.) 



The minor constituents: titanite, apatite, zircon and iron-ore (magnetite 

 and pyrite) are rather abundant, especially magnetite with nuclei of pyrite. 



The plagioclase shows zonal structure, but the borders between the zones 

 are not distinct. The contents of An increase from the periphery to the 

 centre. According to a series of determinations of the extinction «' in 

 sections -l the axis a, the exterior zones correspond with labradorite 

 An.-,5 — >• Anr,7 and the central part corresponds with bytoiv)iitc An7o — ^Ang-, 

 sometimes raising up to anorthitc Anss — )- An.,o in small central nuclei. 

 Special attention is drawn to the peculiar intergrowth between the basic 

 plagioclase and quartz. (Fig. ii.| 



