ART. 11 EOSSITE AND METAHOSSITE FOSHAG AND HESS 11 



(probably inherited from the rossite) it breaks easily into flat, flaky 

 grains. These under the microscope are clear and homogeneous. 

 This platy cleavage makes it difficult to obtain good quantitative 

 measurements of its optical properties. Like the rossite the cleavage 

 flakes show the emergence of an optic axis with a very high disper- 

 sion. The indices of refraction are considerably higher than those of 

 rossite. Only a was within the range of the oils available and was 

 found to be 1.840, ft and y were both somewhat higher than 1.85 but 

 could not be measured directly because the ease with which the 

 mineral dehydrated and melted prevented the use of piperine-iodide 

 melts. The birefringence is high and so far as could be determined 

 the minerals showed no pleochroism. 



EELATION OF ROSSITE AND METAEOSSITE TO OTHER 



MINERALS 



There are no known vanadates having the composition of these 

 two minerals nor any arsenates or phosphates similar to them. They 

 are, however, members of a series with the other known calcium 

 vandates found in nature, hewettite, and pascoite. Tripling the 

 formulae of rossite and metarossite brings out the following inter- 

 esting relation : 



Hewettite 1 CaO. 3 V2O5. 9 aO. 



' Pascoite 2 CaO. 3 V2O3. 11 aO. 



Rossite 3 CaO. 3 V2O5. 12 H2O. 



Metarossite 3 CaO. 3 V2O5. 6 H2O. 



The relation of metarossite to rossite is not entirely clear. It is 

 possible that in common with many other minerals with a decided 

 platy cleavage the water content is variable and that the compound 

 can lose water without any great change in its molecular structure. 

 The ratios for the two hydrates show, upon analysis, such good 

 agreement with the theoretically required amounts without any evi- 

 dence for any intermediate steps that it seems possible that we are 

 dealing here with two distinct hydrates and not with a continuous 

 series. Even were this not the case it is deemed advisable to separate 

 the two compounds in mineral nomenclature in order to avoid 

 confusion, the properties of the two substances being so greatly 

 different. 



SYNTHESIS 



Both pascoite and rossite have been synthesized by Waldemar T. 

 Schaller ^ by heating hewettite suspended in water with precipitated 

 calcium carbonate on the steam bath and allowing the clear solution 



* Fnpublislied data. 



