GEOLOGICAL OCCURRENCE. 



31 



pegmatites and will be referred to in the succeeding pages shortly as 

 pegmatites. 1 



By far the majority of pegmatites are composed, like ordinary 

 granite, of quartz, felspar and mica ; but on account of the gigantic 

 scale on which the crystals have developed, many comparatively rare 

 minerals have been detected in pegmatites which have not been noticed 

 in ordinary granites, possiblj because of the small size of their crystals 

 in the latter rock ; others are possibly peculiar to pegmatites, and art 

 due to the special conditions (referred to below) under which pegma- 

 tites have been formed. The following minerals have been noticed in 

 Indian granite-pegmatites :— 



Albite. Lepidolite. 



Allanite. Leucopyrite. 



Amazon-stone, Magnetite. 



Apatite. Moonstone. 



Automolite. Muscovite. 



Beryl. Orthoclase. 



Biotite. Pitchblende. 2 



1 Coarse-grained felspar-rocks (syenite-pegmatite) occurring near the village 

 of Karutapalaiyam in the Coimbatore district, Madras Presidency, contain crystals 

 of muscovite3 to 4 inches across, associated with corundum, automolite and chryso» 

 beryl, but the veins are not now worked for mica. These rocks and the associated 

 elseolite-sjenites are described in a separate memoir. (Mem. Ceol. Surv. In J., 

 XXX, pt. 3 (1901). 



- The following analysis of pitchblende from the Singar mica mines, Gaya dis- 

 trict, has been made by Mr. W. R, Criper, A.R.S.M., F.C.S., of Messrs. 

 D. Waldie & Co., Calcutta :— 



Oxide of Uranium ...... 



Alumina and oxide of Iron (containing '35% P 2 6 ) 



Sulphide of Lead 



Sulphide of Tin 



Lime , . 



Magnesia 



Siliceous matter . 



Combined water . 



Salts of alkalies (by difference 



79-55 

 335 

 9-96 

 120 



•30 

 trace 

 2-30 



2'90 



•44 



IOO 



( 2J ) 



