38S On SODALITE, a 



new 



fented rectangular prifms, terminated by planes, meafuring, 

 with the fides of the prifm, no and 70 8 or nearly fo, — a 

 form which belongs to a rare mineral, known by the name of 

 Sahlite, from Sweden. He further obferved, intermixed along 

 with this, another material 5 and after fome trouble, fucceeded 

 in detaching a mafs, prefenting a regular rhomboidal dodecahe- 

 dron. It was to this form that Mr Allan had previoufly re- 

 quefted his attention. 



Some time before this invefligation, M. de Bo urn on had 

 examined a mineral from Sweden, of a lamellated flruc"lure, 

 and a greenifh colour, which, he found, indicated the fame 

 form. From this circumftance, together with fome external 

 refemblance, which flruck him, he was induced to conclude, 

 that our mineral was a variety of that fubflance. 



To that fubflance the name of Swedifh natrolite had been gi- 

 ven, in confequence of the invefligation of Dr Wollaston, 

 who found that it contained a large proportion of foda. 



There are few minerals, however, that are fo totally diflinct 

 in their external characters as the natrolite of Klaproth, and 

 the fubflance we are now treating of. The mineral examined by 

 Klaproth occurs at Roegan*, on the Lake of Conflance, in 

 porphyry-flate, coating the fides of veins and cavities in a ma- 

 mellated form, the texture of which is compact, fibrous, and ra- 

 diated \, the colour pale yellow, in fome places paflmg into 

 white, and marked with brown zones. Hitherto it had never 

 been found in a flate fumciently perfect to afford any indi- 

 cations of form. Lately, however, M. de Bournon was fb 

 fortunate as to procure fome of it, prefenting very delicate 

 needleform cryflals, which, by means of a flrong magnifier, 

 he was able to afcertain, prefented flat rectangular prifms, ter- 

 minated by planes, which, he thought, might form angles of 



6o° 



* It has been obferved alfo by Profeflbr Jamison, in the flcetz-trap rocks- 

 behind Burntifland. 



