ORDER VI. AXOTOMOUS KOUPHONE-SPAR. 247 



rieties to which he has given tlie name of Tessclite, the 

 phenomena of double refraction cannot be explained upon 

 the supposition of a single axis, and that even the proper- 

 ties of the mineral are not uniform in this respect through- 

 out the whole mass, but that it appears composed of va- 

 rious parts acting differently upon light. It will depend 

 upon a future accurate examination of the crystalline forms 

 and other properties of this substance, in comparison with 

 these observations, whether they will concur in fixing the 

 limits of the species, or whether this will depend solely 

 upon the optical structure of the mineral. The varieties 

 from Utb'n, and from the Seiseralpe in the Tyrol, evident- 

 ly belong to the preceding species. 



2. According to two analyses by BERZELIUS, referring 

 to L, the Apophyllite from Utb'n, and 2., the Tesselite 

 from Faroe, and one by STRO MEYER of 3., the variety 

 from Greenland, the present species appears to consist of, 



Its chemical formula, according to RERZELIUS, is K Si 4 

 + 8 Ca Si 2 +32 Aq, which corresponds to the ratios of 

 potash, lime, silica, and water = 5-26 : 25-40 : 53-18 : 16-16, 

 no attention being given to the small portion of fluoric 

 acid. Before the blowpipe it first exfoliates, then intu- 

 mesces like borax, and melts at last into a white vesicular 

 globule. It is easily dissolved by borax. It is positively 

 electrified by friction, not by heat. It likewise exfoliates 

 in acids, and its powder forms a gelatine with them. 



3. Like the preceding species, the present one occurs in 

 vesicular cavities of trap-rocks, and in beds in ancient rocks, 

 associated partly with other species of the present genus, 

 particularly hexahedral Kouphone-spar, and with rhombo- 

 hedral Quartz, partly with hemi-prisinatic Augite-spar, oc- 

 tahedral Iron-ore, &c. 



