Calcium Metasilicate. 107 



without recognizable crystallographic grouping. The contact 

 between the natural and pseudo form was sharp, indicating 

 that the transition had taken place without any intermediate 

 stage. 



In a second experiment, natural wollastonite was heated in 

 the electric furnace to 1260° and thus changed in the solid state 

 to pseudo-wollastonite. The resulting mass consisted again of 

 grains of the pseudo form, irregularly arranged, although indi- 

 cations of the original fibrous wollastonite texture are still 

 indistinctly shown. 



The conditions were altered in still another experiment by 

 heating artificial wollastonite crystals, which had been obtained 

 by crystallizing the silicate glass, to the inversion temperature 

 (1190°) for about an hour. The resulting preparation was 

 instructive in showing the paramorphic change in its incipient 

 stage. The original larger crystals were filled "with particles 

 and clusters of the pseudo-form, arranged without apparent 

 regard to the host. Had the preparation been allowed to 

 remain at the inversion temperature for a longer period of 

 time, the change would undoubtedly have progressed until all 

 original wollastonite fragments had been completely replaced 

 by innumerable pseudo-wollastonite grains. 



As the above experiments were made with cleavage fragments 

 of natural and artificial wollastonite which are not so well 

 adapted to. show paramorphism as crystals, artificial crystals of 

 wollastonite obtained from the calcium vanadate flux were 

 heated in the electric resistance furnace above the inversion 

 temperature, and the product examined. The original crys- 

 tals were elongated parallel to the axis of symmetry (b) and 

 were bounded chiefly by forms of the orthodome zone with 

 perhaps the unit prism and unit clinodome forms. After the 

 alteration, each one of the original wollastonite crystals was 

 found to have changed entirely to one pseudo-wollastonite 

 individual alone, and rarely to two or more grains, as is usually 

 the case, a remarkable fact which may be due perhaps to the 

 minute size of the original crystals and to the equality of specific 

 volumes of the two forms. In one instance a basal section of 

 the pseudo-form was contained in the orthodiagonal zone of 

 the original mineral, while in another plate cut perpendicular 

 to the optic normal, sharp twinning lamellae were visible, the 

 traces of which ran parallel to a unit prism or clinodome form 

 terminating the crystal and making an angle of 29° with the 

 direction of elongation of the simulated crystal. From these 

 and other observations, it is evident that, generally speaking, 

 in paramorphic change the planes of symmetry of the two 

 forms do not coincide. Certain crystallographic directions, 



