Pirsson and Washington — Geology of Red Hill, JV. H. 441 



until the subject of texture is considered. The quartz is in 

 minute grains averaging O02-0"05 mm . 



Texture. — Megascopically the rock has a somewhat fine, 

 sugar granular texture which gives it an aplitic habit. It 

 there appears even granular, but in the section it is seen to be 

 microporphyritic. The feldspars which form the great bulk 

 of the rock are present as phenocrysts and as groundmass. The 

 amount of phenocrysts however is very large, as much, if not 

 more, than of groundmass, and they range in size from the 

 largest mentioned above down to those of the groundmass, 

 which may be only 0"05 ram in diameter. The pattern then of 

 the fabric is given by these very numerous, square to short 

 rectangular microperthites of variable size lying in a very fine 

 microgranular groundmass of quartz and feldspar, in which 

 the quartz predominates. 



Mode.— The actual mineral composition is readily told from 

 the chemical composition, since the amphibole, feldspars and 

 quartz are the only minerals present in more than mere traces. 

 It is as follows : 



Riebeckite 7 



Quartz 13 



Orthoclase 33 



Albite 47 



Total 100 



Chemical Composition. 

 table : 



-This is shown in the following 



SiO„ 69-51 



A1 2 3 -- 



Fe 2 3 - 



FeO .... 



MgO 

 CaO .... 

 Na 2 .. 

 K 2 0... 

 H 2 + .. 

 H 2 0- .. 

 CO,... 

 Ti0 2 ___ 

 Zr0 2 ... 

 PA ... 

 MnO.... 

 BaO ... 



15-06 

 1-25 

 1-63 

 0-05 

 0-31 

 6-02 

 5-48 

 0-23 

 0-11 



none 



0-29 



0-01 



tr. 



? 



none 



II 



HI 



IV 



V 



VI 



76-49 



73-35 



76-01 



73-93 



1-159 



11-89 



1438 



11-96 



12-29 



•148 



1-16 



1-96 



2-06 



2'91 



•008 



1-56 



0-34 



n.d. 



1-55 



•022 



tr. 



0-09 



tr. 



0-04 



•001 



0-14 



0-26 



0-26 



0-31 



•005 



4-03 



4-33 



4-46 



4-66 



•097 



5-00 



5-66 



4-73 



4.63 



•059 



0-38 



? 



0-28 



0-41 







0-12 



9 











tr 



tr. 



0-18 



tr. 



.004 



Total 99-95 100-77 100-37 99-76 100-91 



