BY H. C. RICHARDS. 



207 



the pyrites and felspar in admixture form a description, 

 of alum which l)y its crystallisation causes the face of the 

 stone to slip off, just as frost does. When the rain can wash 

 over the face this alum is carried away rapidly and does 

 not do the same amount of mischief.'' 



In all the above occurrences the material seems to be 

 associated with sedimentary rocks. 



The occurrence of " alum " in association with trachytic 

 breccia has been noted by Dr. Jensen at Mt. Flinders, near 

 Ipswich* 



He writes :■ — '" On the south side of the niountain, 

 fibrous Alum fills the joint cracks, and occurs as an excres- 

 cence on the rock. This is piobably because the rock (breccia) 

 is rich in sulphur, which bysome process is being oxidised, 

 and is reacting with the products of decomposition of the 

 felspar." 



Through the courtesy of the Minister for Mines (Hon. 

 A. Jones, M.L.C.) and the Chief Government Geologist 

 (Mr. B. Dunstan) I have been enabled to examine this 

 deposit and to make use of the accompanying analysis. 



The deposit occurs on portions of the floors of fairly 

 extensive caves in the trachyte breccia and in cracks and 

 joints on the rock forming the walls of the caves. The 

 deposit is very limited in size and some of the more coarsely 

 crystalline and pure material yielded on analysis by the 

 Agricultural Chemist the following results : — 



Loss at 100°C. 

 Loss on ignition 

 Alumina 

 Ferric oxide . . 

 Lime . . 

 Magnesia 

 Soda . . 

 Potash . . 

 Sulphur trioxide 



|The sulphur trioxide lost here was deducted. 



Percentage 



13.04 



22.631 



13.95 



tr 



1.70 

 nil 

 4.07 

 3.44 

 41.45 



100.28 



This analysis gives a composition corresponding to 

 (Na2,K2)0. AI2O3. 5SO3. I2H2O. This does not correspond 

 with the analysis of any of the common alums recorded by 

 Dana. Some of the material is exceedingly fibrous and 



*Proc. Linn. See, N.S.W.,-xxxiv, p. 76. 



