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XXXVIII. 



ON A VAEIETY OF FINITE OCOUEFJNG AT BALLYGOEUS, 



(JO. DUBLIN. 



By LOUIS B. SMYTH, M.A., Sc.B., 

 Lecturer' in Palaeontology in the University of Dublin. 



[Read Februauy 28. Published Apml 13, 1922.] 



Introduction. 



Some montlis ago Mr. J. 0. Davison, of the Engineering School, Trinity 

 College, Dublin, brought me for identifieation a green mineral, found at the 

 old lead mines of Ballycorus. It appears not to have been described before. 



Mode of Occurrence. 

 A vi.sit to the locality showed that the substance occurs in the granite 

 blocks thrown out during mining operations, and lying about in and around 

 the large cutting, near the chimney, at the top of the hill. The excavation is 

 at the junction of granite and schist. All stages can be found between 

 typical granite and a thoroughly green rock. 



Results of Tests. 



The following are the results of tests made on the most translucent, 

 lustrous fragments : — 



Compact. Unctuous. 



H = 2-5. G = 2-780. 



Lustre. — Fatty. 



Colour. — Oil green to pale yellowish green. Translucent. 



Insoluble, and does not gelatinize in hydrochloric or nitric acids, or n 

 caustic potash. 



Decomposed by hot concentrated sulphuric acid, with separation of 

 powdery silica. Alum is deposited when the filtered acid is evaporated. 



In the closed tube gives off water easily, and becomes white. Some 

 fraginents darken. Occasionally decrepitates slightly. 



BB. — Infusible, turns white, and does not colour the flame. With cobalt 

 nitrate gives a strong blue. 



Details of Tests. 



Hardness tests required special care owing to the presence of mimite 

 grains and veins of quartz. The salient angles of chips were used to scratch 

 good cleavage surfaces of selenite, Iceland spar, &c. In one sample, for 



