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aggregations of megascopic crystals embedded in a ground mass, 

 these spheroids being generally characterised by concentric shells 

 composed of one or more of the constituent minerals of the rock. 



The section shows a portion of one of the spherules and some 

 of the ground mass. 



The central portion of the spherule is granular diorite ; the 

 surrounding zones are partly radial crystals of bytownite felspar, 

 a,nd partly felspar and hornblende. 



Similar rocks occur in other European localities. 



