Calcium Metasilicate. 



103 



latter, it may be worth while to call attention to the fact that 

 the value of the inversion temperature as a point of reference 

 in geology is not impaired by the varying complexity in the 

 composition of the magma, inasmuch as this temperature has 

 to do with an equilibrium between two solid states of calcium 

 metasilicate, and has no relation to the solution out of which 

 either form crystallizes. It will of course be slightly affected 

 by pressure in the usual way, and also to some extent by the 

 impurities which, in small quantity, are found in the natural 

 mineral, provided these are really dissolved in it. 



Important Properties of the Two Forms of Calcium Metasilicate. 





Inver- 

 sion 

 Point. 



Melt- 

 ing 

 Point. 



Specific Gravity at 25° 



compared with, water 



at 25°. 



Symmetry. 



Cryst. 

 from an 

 under- 

 cooled 

 melt. 



Cryst. 



from 



Ca(V0 3 ) 2 . 



Mol- 

 ten. 



,„ ,, ., 1 monoclinic 



Vv ollastonite ■{ .. ,, .• 



( optically negative 



( probably monoclinic 

 Pseudo-Wollastonite -j pseudo-hexagonal 

 ( optically positive 



1180° 



1512° 



2-915 



a. 2-914 



b. 2-912 



2-912 



Optical Study. 



In the thin sections which were made from the various 

 preparations of calcium metasilicate, both forms, wollastonite 

 and pseudo-wollastonite, were recognized, and determined by 

 their optical properties alone, their morphological features 

 being too indefinite and inconstant to be of service. For- 

 tunately several of the optical characteristics of the two min- 

 erals differ sufficiently to render the separation under the 

 microscope relatively simple. 



Textually the preparations show considerable variation, 

 although in general the artificial wollastonite occurs in fibrous 

 or long prismatic aggregates, while the pseudo-wollastonite is 

 more coarsely crystalline and granular in appearance. Radial 

 spherulites of wollastonite in which the crystals are elongated 

 parallel to the axis of symmetry (b) were observed frequently, 

 especially in the sections of wollastonite from crystallized 

 glass. 



In size the crystals range from the finest cryptocrystalline 

 aggregates to individuals several millimeters in length. As 



