Serpentine Area and Rhyolites. 261 



100.89 

 Density - 3.881 



The question of the genesis of the corundum and the chromite 

 can be conveniently discussed together, for the association in the 

 Dolodrook district suggests analogies to similar occurrences else- 

 where. In North America, corundum is known both in acid and 

 in basic rocks. The latter occurrence is worthy of comparison. 

 In North Carolina it is found near the margin of peridotite rocks, 

 in which chromite also occurs, and J. H. Pratt, who has studied 

 the occurrence, considers that the origin is best referred to as 

 one of magmatio segregation. Morozewicz further showed experi- 

 mentally that alumina is soluble in a molten, basic glass, and 

 that on cooling the alumina rich magma crystals of corundum 

 crystallized out. 



No excavations have been made in the Dolodrook area to de- 

 te.rmine whether the corundum is in situ or not, but there ia 

 little reason to suspect that it is not, and Professor Skeats tells 

 me tha.t he has found it and chromite distributed in small quan- 

 tities through the rocks of the Heathcote area, in which he has 

 found the larger pieces of corundum. Chromite is recognised 

 both as a secondar}' and an original constituent of igneous rocks, 

 but it would appear the Dolodrook occuiTence most probably 

 indicates a particularly fine example of magmatio segregation, in 

 which the olivine, pyroxenes, corundum and chromite all repre- 

 sent different phasea. 



