604 MK. A. K. COOMAEA-SWAMY ON [Aug. I90O, 



Two or three microscope-sections cut from different parts of this 

 specimen are seen to contain green augite, orthoclase-microperthite, 

 quartz, scapolite, sphene, and iron-ore in different proportions. 

 The scapolite gives negative uniaxial interference-figures, and 

 depolarizes vividly even in thin sections. Grey fibrous decom- 

 position-products are often present. 



A banded, dark rock, collected near by, contains scapolite, 

 augite, quartz, wollastonite, sphene, graphite, pyrite, and calcite. 

 Scapolite is very abundant, and may be recognized by its rectangular 

 cleavage, straight extinction, and negative interference-figure. It 

 is water-clear, but contains some minute lath-shaped opaque inclu- 

 sions and needles of a transparent mineral arranged with their long 

 axes parallel to the vertical axis of the scapolite. The wollastonite 

 occurs in fairly large individuals, which are evidently moulded on the 

 other minerals. It is colourless, and has a moderately high refractive 

 index, but rather weak double refraction. Its biaxial character can 

 be ascertained : the open axial plane is at right angles to the 

 parallel cleavage-cracks. The wollastonite has been sometimes re- 

 placed by a quartz-calcite mosaic which occurs in some small areas 

 between the other minerals, often associated with a residual 

 fragment of wollastonite. Two portions of wollastonite extinguish- 

 ing simultaneously may be thus separated by a fine-grained quartz- 

 calcite mosaic : in some cases no wollastonite is left, in others no 

 trace of alteration is visible in it. 



An even, but not fine-grained, green-and-white rock from the 

 same locality contains the usual pale green ' augite,' orthoclase- and 

 microcline (?)-microperthite, scapolite, sphene, zircon (?), apatite, 

 and graphite. A considerable quantity of this rock was crushed 

 and passed through a mesh with 30 holes to the square inch, but 

 was retained by one with 60. The grains thus obtained were not 

 composite. The pyroxene and sphene were separated by means of 

 cadmium borotungstate, and the pyroxene was then picked out with 

 a camel's-hair brush. More than 3 grammes of perfectly pure light 

 green pyroxene being thus obtained was supplied to Mr. Shepherd 

 for analysis, with the following result : — 



Per cent. 



Si0 2 50-91 



CaO 2441 



MgO -58 



A1 2 3 1-78 



MnO 2-64 



FeO 19-91 



100-23 



Specific gravity = 3*377 



This composition corresponds almost exactly with that of manganheden- 

 bergite, to which species the pyroxene must be referred. Neglecting the 

 alumina and a little of the silica, the formula CaFe(Si0 3 ) 2 is obtained. 



