ZIEGLER, THE RAVENSWOOD GRANODIORITE 9 



result of the rearrangement of two or more adjacent minerals. It is diffi- 

 cult to say just what minerals formed the garnet occurring so extensively 

 throughout the granodiorite, but the following reactions are offered. 



Anorthite + wollastonite = grossularite + quartz 

 CaO,ALA,2Si() a + 2(CaO,Si0 2 ) = 3CaO,Al 2 3 ,3Si0 2 + SiO, 



Anorthite + hypersthene = garnet + quartz 



CaO,Al 2 3 ,2Si0 2 + 2( (MgFe)0,Si0 2 ) = CaO,2(MgFe)0,Al 2 3 ,3Si0 2 + SiO, 



Pyroxene -{- anorthite = amphibole- 



(MgFe)0,(AlFe) 2 3 ,Si0 2 ,2(MgO,Si0 2 ) + 2(CaO,Al 2 3 ,2Si0 2 ) = 2(CaO)(MgFe)0, 



pyroxene molecule -f- garnet + quartz 



(AlFe) 2 3 ,3Si0 2 + 2(MgO,Al 2 3 ,Si0 2 ) + 3Si0 2 



Starting with orthoclase, the following reaction might take place. 



Orthoclase + pyroxene wollastonite + hypersthene -f- 



K 2 0,A1 2 3 ,6S]0 2 + 2( (MgFe) 0,(AlFe) 2 3 ,Si0 2 ) + 2(CaO,Si0 2 )+ (MgFe)0,Si0 2 + 

 water=garnet + biotite + 



H 2 0=2CaO,(MgFe)0,Al 2 3 ,3Si0 2 +2((HK)0,(AlFe) 2 3 ,2Si0 2 )2((MgFe)0,Si0 2 ) + 

 quartz 

 3Si0 2 



Yielding in this last case a complex garnet, biotite and quartz. 



Comparison with the Harrison Granodiorite 



A comparison of the Eavenswood granodiorite with the Harrison grano- 

 diorite as described by H. Eies 6 was made for the purpose of determining 

 any relationship which might exist between the two rocks. Professor 

 Eies says, regarding the Harrison diorite, 



"Throughout its extent, the rock has a pronounced gneissic structure. Strong 

 effects of folding and crushing with the consequent formation of 'augen' of 

 quartz and feldspar are shown. The rock varies from a more or less massive 

 gneiss ... to a mica-schist. The minerals forming the granite are quartz, 

 plagioclase, biotite, hornblende, orthoclase, and in lesser amounts garnet, tita- 

 nite, zircon, apatite, muscovite, and microline. 



"Quartz composes from two fifths to one half of the rock. It occurs in 

 grains and in rounded masses, filling the spaces between the other minerals. 

 The grains are often cracked and show undulatory extinction and zonal struc- 

 ture. Dustlike inclusions are often present and are arranged in more or less 

 parallel rows, which often extend across the cracks from one grain to another. 

 Intergrowths with plagioclase are not uncommon, especially around the edges 

 of the feldspar augen. 



"The plagioclase is rich in inclusions of biotite, apatite, and zircon, but 



* Trans. N. Y. Acad. Scl., vol. siv, p. 80. 



