South -■Vfrican Granites. 



^83 



replaced by the yellowish micaceous " pinite " pseudomorphs. The 

 intermediate stages f)t" the alteration may be well observed. Cordierite 

 appears to be sometimes present in the normal granite, which also 

 contains numerous small zircons, generall) as inclusions in the biotiie 

 where the\ give rise to the usual pleochroic " halos. 



lUl.AW AVd (IRAMTK. 



In the Tati District of Hechuanaland. granite occurs as a modi- 

 fication of the prevailing syenite, and is chiefl) remarkal)le for the 

 amount of apatite it contains.. This mineral sometimes forms cnstals 

 an inch in diameter: for the nu)st part, however, they are of purely 

 microscopic dimensions. They shew not only the usual cross-fracture 

 but also complete dislocation of single crystals into a number of 

 separate fragments dixided b\ p(_)rtions of the enclosing quartz or 

 felspar. Sphene is abundaJit in this rock. It surrounds the iron ores 

 in whitish granular aggregates which, unlike the variety leucoxene, 

 are more or less transparent and shew brilliant interference tints 

 when the sections are sufficiently thin. 



The granites of Rhodesia are notable for the abundance of 

 microline. which is usualb the dominant feLspar. The now well- 

 known Matojjo granite is tvpically composed of microcline. quartz, 

 and biotite with a little magnetite anrl some brownish sphene. The 

 Bulawavo margin of the mass is a hornblende granite with microcline, 

 nligoclase and orthoclase as the felspars. The accessories include 

 large crvstals f)f ai)atite, abtmdant vellowish sphene. a little magnetite 

 anil a good deal of pale \ellow ejiidote. The last named mineral 



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