124 



The best accessible outcrop is on the property of the Port 

 Lincoln Copper-mine, in the hills five miles west-north-west 

 of the township. There the mineral occurs in fissures up to 5 

 cms. wide, traversing the marble. These chrysotile veins are 

 set in massive yellowish-green serpentine, which grades out- 

 wards into the less metamorphosed marble, and evidently, 

 originally, the sites of cracks, probably the effect of shattering 

 by mechanical compression, or possibly arising from contrac- 

 tion consequent on dolomitization and other chemical changes 

 effected in the originally pure limestone. 



IX. WOLLASTONITE. 



So far as I am aware, this mineral has not previously 

 been recorded from South Australia. It is extensively de- 

 veloped as an alteration product of the ancient marble re- 

 ferred to in the preceding paragraph. 



The workings of the Port Lincoln Copper-mine are 

 chiefly confined to a mineralized belt in this marble, and the 

 ore gangue is largely composed of wollastonite. 



As the rock is compact, crystals of the calcium-metasilicate 

 cannot be readily isolated ; nor does its pure white colour aid 

 in discriminating it amongst other minerals present similar in 

 this respect. 



A number of microscope sections prepared of the rock, 

 however, revealed its presence in varying proportions. By 

 judicious selection, masses of almost pure wollastonite rock 

 may be got. 



The resistance to weathering offered by wollastonite 

 allows of its ready detection on the exposed surface of the 

 silicated marble, as where it occurs the weathered surface is 

 rough and jagged. 



Mineralogical Laboratory, 

 University of Adelaide. 



EXPLANATION OF PLATE XXL 



Fig. 1. A lenticular gypsum twin, as found occurring in the 

 subsoil near Glenelg. 



Fig. la. View of same perpendicular to Fig. 1. 



Fig. 2. A spiral twin of gypsum; a common development of 

 preceding type. 



Fig. 2a. View of same perpendicular to Fig. 2. 



Fig. 3. A barytes sand crystal from Hallett Cove. Hadial- 

 tabular aggregates composed of sand grains cemented by about 35 

 per cent, of barytes. 



Fig. 3a. View of same perpendicular to Fig. 3. 



Fig. 4. A barytes sand-crystal as frequently developed at 

 Hallett Covo. produced by multiplication of the number of indi- 

 viduals, contributing to the aggregates, and resulting in an ellip- 

 soidal form, with corrugated surface, resembling a peach-stone. 



Fig. 4a. View of same perpendicular to Fig. 4. 



