MOUNT GEEYLOCK. 

 Analysis No. 567. Feldspar from specimen 709a, T>. f. 188C 



187 



SiO,, 



A1..0,+(F ej 3 <5%) 



MnO 



CaO 



MgO 



Na 2 



K,0 



Ignition 



II 



20. 11 

 trace 

 trace 



f 

 11.00 

 .36 

 .31 



09. S6 



67.83 

 l'.i 92 

 trace 

 trace 



? 

 11.65 

 .25 

 .12 



99.77 



Dried at 105 C. Specific gravity slightly above 2.6545, between 2.6545 and 2.61.' 



At the south end of the top of Ragged mountain in the small isolated 

 schist area (locality 764), the albite gneiss is "coarsely foliated with a 

 wavy structure composed of bands of dark mica, alternating with irregular 

 layers of calcite mixed with quartz and large rounded feldspar crystals. 

 Needles of tourmaline occur occasionally. The albite crystals are not 

 twinned, have a rounded outline, often lie with their longer axes across the 

 foliation of the rock, and contain inclusions of calcite, quartz grains, and 

 flakes of both micas. The groundmass consists of interlacing fibrous 

 layers of muscovite and biotite, little grains of quartz and great quantities 

 of calcite, not in grains but in masses. The calcite sometimes penetrates a 

 large feldspar, breaking it up into isolated cores of feldspar, surrounded by 

 calcite. It is difficult to sav with certainty whether the calcite was formed 

 later than the quartz and mica or contemporaneously with them. It occurs 

 in veindike masses, not in grains ; when it has encroached on the feldspar 

 it does so irregularly and not parallel to the schistosity of the rock, as the 

 quartz and mica do; rarely tongues of calcite cut in two inclusions of 

 quartz in the feldspars — it seems rather therefore to be pseudomorphous — 

 replacing quartz as well as feldspar." 



Towards the top of Grreylock and along the central ridge the feldspar 

 crystals are very minute, and are not rounded. (Thus at locality 861 on 

 the Greylock road.) 



1 Mr. Wol ft adds for comparison the analysis of a colorless albite from Kirabinsk, Urals. SiOs 

 68.45, AliOj 18.71, FeO 0.27, NaO s 11.24, K.O 0.65, CaO 0.50. MgO 0.18. Total 100. Spec. grav. 2.624. 



