GEOLOGY AND PETROGRAPHY OF THE PROSPECT INTRUSION. 539 



angles up to 16°. Pericline twinning is occasionally seen. 

 The orthoclase exhibits carlsbad twinning, but is too decom- 

 posed for an accurate determination as to whether it is 

 anorthoclase or not. 



Pyroxene. 

 This mineral is present in relatively small quantity and 

 usually occurs as small idiomorphic crystals, wholly or 

 partly enclosed in the felspars. It is usually a pale green, 

 non-pleochroic diopside, with in some of the larger crystals 

 an inner zone of purplish-brown feebly-pleochroic augite. 

 A thin outer zone of segyrine-augite is occasionally present. 

 In one slide only, numerous small idiomorphic crystals of 

 aegyrine-augite occurred, associated with much biotite. 

 The pyroxenes are much less altered than the felspars, pro- 

 ducing chloritoid decomposition products. Some crystals 

 have been partly replaced by calcite. 



Other Minerals. 

 These are all similar to those described as occurring in 

 the pegmatite veins, but are, for the most part present in 

 less quantity. 



The following is an analysis of the aplite by J. C. H. 

 Mingaye with the norm calculated from it: — 



lalysis, coarse A 



plite. Mol 



ecular rati' 



o. Norm. 



% 



Si0 2 



58*82 



980 



Quartz 



1*92 



A1 2 3 



16*91 



166 



Orthoclase 



17*79 



Fe 2 3 



2*40 



015 



Albite 



56*59 



FeO 



4*59 



064 



Anorthite 



6*95 



MgO 



0-88 



022 



Corundum 



0*10 



OaO 



2*42 



043 



Hypersthene 



6*82 



Na 2 



6-74 



109 



Magnetite 



3*48 



K 2 



2*96 



032 



Ilmenite 



2-13 



H 2 100 0. 



0*561 



+ 1-98) 



141 



Apatite 



0*62 



H 2 100 O. 



Calcite 



1*20 



co 2 



0-54 



012 



H0 2 and CI 



2-55 



Ti0 2 



p 2 o 5 



1-14 

 0*34 



014 



002 







Total 



100*15 



CI 



0*01 



, . . 









MnO 



0-13 



001 







Total 



100-42 





