50 AUSTKALASIAN ANTARCTIC EXPEDITION. 



the decrystallisation of the felspar. Associated with the epidote is clinozoisite and 

 zoisite, which are often intergrown in the one crystal. Clinozoisite is the more abundant, 

 and is readily detected by the ultra blue polarisation colour. Like the epidote, two 

 cleavages are present, and it is found to have approximately straight extinction with 

 reference to one cleavage and a large extinction with reference to the other. In several 

 instances the optic axial plane was determined to be perpendicular to the cleavage, 

 and the small curvature of the bar in the interference figure in sections normal to an 

 optic axis indicates a large optic axial angle. Clinozoisite may also be bordered by 

 finely granular material. The zoisite, with its bluish-grey polarisation colour, is distinct 

 from the clinozoisite and the epidote. Wherever determined the optic axial plane is 

 normal to the cleavage indicating the variety zoisite ft. 



Lawsonite has been found in some sections in large individuals and in small veins. 

 In the development of some of the crystals a brown micaceous mineral, like poorly- 

 developed biotite, has been thrown out along the cleavage planes. This fact may be 

 interpreted as evidence of the contemporaneous development of the intergrown lawsonite 

 and biotite reported in the lawsonite amphibolites. 



Green pleochroic chlorite is present, and may show the usual anomalous polarisation 

 colour or a pale-greenish-white colour between crossed nicols. The amount of chlorite 

 is very small in some cases and in others the aggregates may be radial. A white 

 mica is present, which is probably muscovite. When best developed it is clear and 

 colourless, with cleavage and the usual absorption. Sometimes it presents a confused 

 and ragged appearance with the laths set in a criss-cross manner. 



In similar association to the white mica is scapolite, with its low refractive index 

 and brilliant polarisation colours. It has been identified by its uniaxial and negative 

 character. How much of the brightly polarising mass is scapolite and how much is 

 white mica must remain an unsettled question. Calcite is sometimes found in plates 

 of irregular outline, and a small segregation of calcite is present in one instance. Grains 

 of pyrite and magnetite are nearly always present, and in several cases the pyrite is 

 visible macroscopically. 



In this mineral aggregate there is sometimes a clear felspar which is either untwinned 

 or finely lamellar twinned. The refractive index is moderately low, but always above 

 Canada balsam. In No. 628 (5) the extinction angle goes up to 18 when measured in 

 sections with cleavage but without twinning. It is therefore interpreted as either 

 oligoclase or andesine. In this instance the felspar of the adjoining amphibolite is quite 

 clear and recrystallised, and seems to be identical with the clear felspar in the saussurite. 

 The latter is sometimes fringed with the clear felspar which then comes in contact with 

 the clear felspar of the amphibolite. An extinction angle of 17 can be measured among 

 the grains in the amphibolite. Hence, if both are identical the determination must be 

 andesine. 



