Crystallization of Parisite. 545 



There remain but two sensible differences between the two 

 substances ; synchisite has a slightly lower specific gravity ; 

 and its chemical composition shows the presence of exactly one 

 molecule of CaC0 3 more than is present in parisite. It is 

 hardly possible that this large difference in composition can 

 rest in analytical errors ; on the other hand, it is quite impos- 

 sible for the writers to believe that two substances with such 

 a profound chemical difference as this could be so nearly 

 identical in all their physical properties. The following con- 

 sideration is offered as a possible interpretation of the matter. 



In describing the crystals of synchisite Flink states that 

 many of them show an enlarged central }Dortion with forms 

 and luster differing from the smaller crystals and with slightly 

 altered optical character. This is a character common to the 

 larger crystals. Now there is no statement in the paper of the 

 quality of the analyzed crystals. Are we not justified in 

 believing that the analysis material contained enough of this 

 altered substance which might well be CaC0 3 to produce the 

 differences found % The alteration would tend to lower the 

 specific gravity, so that this difference too would be accounted 

 for. A new analysis of perfectly fresh synchisite can alone 

 settle the question. 



Microcline. — Microcline in well-formed crystals of orthoclase 

 habit makes up the greater part of the porous material near 

 the great central pocket. The crystals range from a diameter 

 of two and a half centimeters downwards to mere crystal 

 specks ; they are, however, very constant in habit, presenting a 

 remarkably cuboid form due to the dominant development of 

 the base, clinopinacoid and orthodome ; prism and unit pyramid, 

 the only other forms found, being very subordinate in size. 

 The faces are smooth and give fairly good reflections of the 

 goniometer signal. The albite twinning, shown by microscope 

 study to be universally present, is not apparent on the exterior 

 of the crystals ; its presence makes the crystals sensibly mono- 

 clinic however, and the measurements obtained approximate to 

 those of orthoclase. Well-formed Baveno twins are seen in a 

 few specimens, but most of the crystals are in clusters without 

 apparent definite relation of the constituent individuals. The 

 color of the microcline is white to pale ivory-yellow. On faces 

 of the prism there is often a secondary coating of colorless 

 glassy feldspar in parallel position to the main crystal, which 

 the microscope shows to be also microcline, although its 

 appearance strongly suggested the growths of albite so common 

 on orthoclase from numerous localities. 



Orientated sections, cut from the freely developed crystals 

 of the pocket lining and from some of the larger crystals with- 

 out, show that the microcline is twinned after the albite law 



