32 AUSTRALASIAN ANTARCTIC EXPEDITION. 



paler hornblende. Such hornblende becomes very distinct between crossed nicols 

 in virtue of its bright interference colours. Chlorite is associated in some parts with 

 the hornblende in a way suggesting that the chlorite gradually passes into hornblende. 

 In other parts there is a transition between epidote and hornblende. The greater part 

 of the felspar is cloudy and saussuritised. Arising out of the saussuritised part the 

 secondary plagioclase can be seen. Epidote may be found in the saussuritised mass 

 as well as magnetite, scales of hematite, and micaceous products. In the same connection 

 radial aggregates of a fibrous cloudy mineral are found with very low refraction, double 

 refraction about the same as quartz and oblique extinction with a small extinction 

 angle. This is probably stilbite, one of the zeolite group, which is much better developed 

 in the next slide. Sphene possesses rather a deeper clove-brown colour than usual, 

 and is almost free from the magnetite core. No. 5 may be called an amphibolite. 



When the joint planes, which are lined with epidote, are exposed by weathering, 

 they form a rock wall brilliantly green in colour. Some of the hand specimens are faced 

 with the green epidote about 1mm. thick. In these specimens the rock can be seen 

 to become very distinctly richer in epidote as the face of the joint plane is approached. 

 There is a segregation towards a plane in this case, whereas in a subsequent example, 

 the epidosite in the band No. 629, the segregation is apparently towards a centre. 



Some of the joint planes are characterised not so much by the green epidote or by 

 fluorite as by a radiate, fibrous mineral of pinkish-white colour. A thin section was 

 cut as close as possible to the face of one of these joint planes in order to include the 

 fibrous mineral, and has been found to be very interesting. Not only are the relation 

 of epidote, chlorite, and hornblende clearer than in the preceding slide, but stilbite, 

 fluorite, and lawsonite are present. The radiating fibrous aggregates are prominent in 

 the section and the mineral is mostly clear and colourless, though cloudy in part. Its 

 refractive index is less than Canada balsam, and its polarisation colours are a little 

 higher than those of felspar. It has an extinction angle up to 10, and, as the prism 

 axis is the direction of the fastest ray, it can be determined as stilbite. Grains of 

 nuorite are not infrequent. Sometimes they show a trace of blue colour, and they 

 may be crowded with minute needles of a green mineral with oblique extinction, 

 probably pale hornblende. The development of chlorite and epidote from hornblende 

 is more noticeable. The green hornblende first passes into colourless hornblende, which 

 may be replaced by an aggregate of epidote and chlorite. Grains of fluorite may be 

 found in these aggregates. The hornblende also undergoes a change through colourless 

 hornblende, with oblique extinction, into the brightly polarising lawsonite, with its 

 straight extinction. Aggregates of lawsonite may fringe the radial groups of stilbite. 

 Some of the lawsonite aggregates resemble scapolite in appearance, but the refractive 

 index is too high, and wherever an interference figure is obtained it is biaxial in character. 

 There is here, perhaps, more clear felspar than in the normal slide. The refractive 

 index of this clear felspar is sometimes above and sometimes below Canada balsam, but 

 it is always very close to it. The clear felspar, therefore, belongs to the albite end of 

 the lime soda series. 



