162 VOLCANIC AREA OF EAST MORETON, ETC., DISTRICTS, Q., 



of phenocrysts, and in minute granules plentifully scattered 

 throughout the base, (b) enstatite in phenocrysts; (iv) magnetite 

 in minute idiomorphic grains abundantly distributed throughout 

 the base; (v) serpentine from the alteration of olivine; (vi) green- 

 ish volcanic glass, interstitial between microlites of felspar and 

 granules of augite and magnetite of the base 



(3) Name : Olivine Enstatite Basalt. 

 Basalt obtained at Sellin's, on the Byron Ck slope of Mt. Mee 



Handspecimen is a black rock in which olivine can be seen 

 with the naked eye, and with a pocket lens its abundance becomes 

 very evident. 



Microscopic examination. — -(1) Texture: (a) noncrystalline; 



(b) fine-grained, porphyritic; (c) ophitic. 



(2) Constituents (inorder of decreasing abundance). — (a) Labra- 

 dorite in lath-shaped crystals of highly varying dimensions, some 

 being of the size of phenocrysts, and some very minute indeed; 

 (6) augite in rounded granules scattered throughout the rock; 

 .several adjacent granules are sometimes in optical continuity 

 though separated by felspar (ophitic structure); variety diopside : 



(c) olivine in hexagonal sections, perfectly colourless except when 

 decomposing to serpentine; granules of augite commonly cluster 

 round the olivine; secondary magnetite is also found round it ; 



(d) ilmenite, which is more plentiful than magnetite, occurs in 

 characteristic tables and rods; (e) magnetite (i) idiomorphic, (ii) 

 dusty; the former variety is primary, the latter secondary; mag- 

 netite is commonly contained as inclusions in all the other 

 minerals including olivine ; {/) idiomorphic phenocrysts of 

 enstatite; (y) decomposition products. 



(3) Order of consolidation normal. 



Magnetite and ilmenite 



Olivine 



Enstatite 

 Augite (Diopside) 



Labradorite 



Secondary : Magnetite surrounding olivine; serpentine from 

 alteration of olivine and augite. 

 Name: Olivine Enstatite Basalt. 



