• BY H. C. RICHARDS. • l05 



resisted better iu that it lost less weiglit of material, but its 

 abraded surface was not so smooth as that of the "' trachyte." 



A chemical analysis of a representative sample of the 

 rock from the qiiany was made some years ago by Mr. N. 

 Christensen of the Agricultural Chemical Laboratory. The 

 results are shoAvn in the table on page 150. 



The norm gives the following calculated mineralogical 

 composition : 



Quartz . . . . . . 34.1-t per cent 



Orthoclase . . . . . . 17.24 ,, ,. 



Albite 2.5.1.5 .. .. 



Anorthite 11.68 ., ,. 



Coruruluin . . . . . . 1.84 ,, ,. 



Hj'per.stliene . . . . . . 7.65 ,. ,, 



-Magaetite 0.93 „ ,. 



Ilmenite . . . . . . 0.76 ,, ,, 



* Apatite 0.67 „ „ 



Pyrites . . . . . . . . p.n.d. 



Water 0.42 „ „ 



100.48 

 CIas.sification : I. 3.2.3. Tehamose. 



Although the norm is only the calculated and not 

 the actual mineralogical composition it ser\"es to show the 

 great preponderance of light-coloured minerals and the 

 paucity of ferro-magnesian minerals in the stone. 



The density is 2.59 which is on the low side for a granite : 

 as a result the stone would weigh ir)21bs. per cubic foot. 



Mt. Crosby " Granite.'' 



This handsome stone occurs in the neighbourhood of 

 Mt. Crosby, and the material used in Brisbane was obtained 

 from Bendley"s selection, boulders 01J3' being worked. 



The ■• granite "' is a dark green rock of medium grain 

 and it has a much greater j^roportion of dark ferro-magnesian 

 minerals than either the Enoggera granite or the Greymare 

 granite. 



It may ])e seen in the base of the Executive Building 

 in alternate courses with Enoggera granite. An opportunitj- 

 exi.sts therefore of comparing it with the Enoggera granite, 

 and it is seen to be free from pyrites and to be much darker. 

 It has been both rock -faced and patent-axed, and in both 

 modes of work it looks well. 



