164 THE PYROXENE GRANULITES COLLECTED 



1684. Pyroxene Granulite, Erratic (Cape Royds). 



In hand-specimen a dark green, greasy-looking rock ; it is muck silicified and is 

 slightly foliated. Quartz and a dark ferro-magnesian mineral can be recognised. 



Under the microscope the fabric is granulitic ; the grainsize is even and medium. 

 A marked degree of foliation is shown by the biotite, pyroxene, and quartz. The 

 biotites have their longer axes in a general parallel direction, as also have the pyroxenes 

 to a lesser degree. The quartz grains are elongated parallel to the same direction. 



The minerals present are : quartz, felspar, biotite, pyroxene, apatite, sphene, pyrites, 

 and zircon. 



Quartz is most abundant in allotriomorphic grains. It shows shadowy extinction 

 and has undergone a considerable amount of granulation. Felspar is fairly abundant. 

 It is mostly untwinned but occasional grains are twinned after the albite law. It is 

 in subidiomorphic grains, slightly decomposed and with numerous inclusions. Its 

 R.I. is higher than that of quartz. Biotite is present in some quantity in very ragged 

 allotriomorphic grains. It is moulded on both the pyroxene and felspar. In most 

 cases where it is moulded on the pyroxene there is a fairly well-marked line of division 

 between the two minerals ; in a few cases, however, the line is not easily distinguished, 

 and it appears in these cases as if the biotite may be the result of an alteration of the 

 pyroxene. The minerals of the rock show considerable granulation, and this is possibly 

 a case of alteration such as described by Parsons.* 



Pyroxene is not very abundant in colourless, allotriomorphic grains. Sphene, apatite, 

 pyrites, and zircon are sparingly present. 



960. Pyroxene Granulite, Erratic (Cape Royds). 



The hand-specimen is a dark-greenish, hard, and somewhat silicified rock. It is 

 very fine-grained and shows very little foliation. Quartz and a dark ferro-magnesian 

 mineral can be recognised. Under the microscope the fabric is granulitic and the 

 grainsize even and medium. Foliation scarcely noticeable. (Plate I, Fig. 1.) 



The minerals are : quartz, pyroxene, felspar, sphene, zircon, apatite. Quartz is 

 in irregular allotriomorphic grains, and is easily the most abundant mineral. It is 

 quite clear and free from inclusions, shows shadowy extinctions, and is considerably 

 granulated. Felspar is abundant in subidiomorphic sections twinned mostly after the 

 albite law and occasionally after the Carlsbad. Its R.I. is a good deal higher than 

 that of quartz. Extinctions in sections perpendicular to albite twins go up to about 

 32°. It is then a basic labradorite. It shows shadowy extinctions ; it is only very 

 slightly dusted with decomposition products. Pyroxene is in irregular-shaped grains and 

 columnar sections. It is colourless and without many inclusions. Sjmene is plentiful and 

 is mostly included in the quartz and pyroxene. Small zircons and apatites are present. 



1537. Pyroxene Granulite, Erratic (Cape Royds). 



In hand-specimen a greyish-green holocrystalline rock ; medium to fine-grained. 

 No foliation visible. Quartz is recognisable, and the ferro-magnesian mineral is a rather 

 light green in colour. 



Under the microscope the fabric is granulitic ; grainsize even and fine. Foliation 

 apparent by the direction of elongation of the minerals. (Plate I, Fig. 2.) 



The minerals present are : pyroxene, felspar, quartz, sphene, zircon, and carbonate. 



Pyroxene is abundant in irregular grains, very light in colour. Felspar is in allo- 

 triomorphic grains twinned after the albite, Carlsbad, and pericline laws. The combina- 

 tion of albite and pericline laws gives a cross-hatching appearance very like microcline. 

 It is moulded on quartz and sometimes pyroxene ; it is quite fresh. Extinctions in 

 symmetrical sections go up to 33°, and it is therefore a basic labradorite. Quartz 



* James Parsons, B.Sc, " The Development of brown mica from augite, etc.," Geol. Mag., 

 1900, p. 310. 



