58 MIDDLEMISS: TIIK (JKOl.OGY OF IDAR STATE. 



somewhat like the last-described, but with slightly more crystalline 

 structure. It contains much pyroxene, which, though usually 

 present in Irregular -rains poikilitic over large areas as in many 

 of the other compact varieties, occurs also sparingly in roughly 

 isomorphic shapes, giving basal sections with characteristic cleavage, 

 and other elongated sections with extinction angles X A C =-42 , 

 which is characteristic- of diopside. The rest of the ground-mass 

 shows many elongated laths of wollastonite, with pearly lustre, 

 parallel iibration. positive elongation, etc.. exactly as has been 

 described in the eale-gneiss from CoKvara. f& (12141), (see ]>. 17). 

 There is a considerable quantity oi sphene in groups of small roughly 

 crystalline grains. Thus the matrix of the whole rock will be seen to 

 be practical lv identical with that, of the (Jolwura rock except that it is 

 finer grained'. Scattered about the ground-mass either in rough layers 

 or in detached individuals lie large prisms or roundish grains of 

 idocrase of a bright brown colour. They are as much as an inch m 

 length and J -inch diameter in the first specimen and more rounded m 

 tluTseeond. In thin section they can be seen to enclose poikilit ieally 

 a great number of pyroxene grains, and are in all their optical 

 characteristics identical with the idocrase described in specimen 

 ,-,'V (12152) from near Nadri. In addition to the above-deter- 

 mined minerals in the rock, there are also some dusty amorphous 

 areas representing some altered mineral which cannot be deter- 

 mined. It may partly be leucoxene passing into sphene. with 

 which it appears to be associated in the thin section. There is a 

 patch of calcite in one slide of the second example. 



It seems certain that the development of large idocrase crystals 

 in this rock, its generally coarser grain than 

 Special cent act mete- t ] ie average Mundeti rock, the presence of 

 motphian. indicated. pyroxene and wollastonite and the absence of 



quartz and calcite (except one patch of the latter in one place) 

 indicate special contact metamorphism induced by the proximity 

 of the intrusive Idar granite along this N.W. end of the hill-mass ; 

 so that there has been produced what is practically a calc-gnciss 

 closely resembling the Colwara rock 3 2 8 5 8 and with idocrase in it 

 as in the Nadri rock, 3 \V It appears to be a valuable link con- 

 necting the Mundeti series with the calc-gneiss series. 



Finally we nave m otneT P arts of tne series at some distancc 

 from the Idar granite occurrences, specimens, 



Jg%£A "'" ■* ™ M ; » id M fr01 " near Malasa ' 



