1820.] M. Stromeyer on Polyhalite. 429 



solution, as from the facility with which it is melted and reduced 

 to an opaque mass, and likewise from the similarity of the spe- 

 cific gravity of both these minerals. 



A more exact chemical analysis, however, has brouo-ht for- 

 ward both facts and arguments that are in direct opposition to 

 this hypothesis, and most satisfactorily prove that the fossil of 

 which we are treating is completely different both from glaube- 

 rite and anhydrite. For it is evident, as will appear from the 

 experiments I am now about to give, that there was no sulphate 

 of soda, but that it consisted of sulphate of lime both combined 

 ■with water and in an anhydrous state, of anhydrous sulphate of 

 magnesia and of sulphate of potash, in which latter respect, it 

 differs from every fossil of this class. 



This being the case, I had no doubt whatever as to this fossil 

 constituting a new and unknown species of the class of salts 

 which I propose to distinguish by the term polyhalite, since it 

 particularly differs from the rest of this class of fossils in the 

 number of its constituent parts. 



Mineralogical Description of Polyhalite. 



Previously to giving a chemical analysis of this fossil, it will 

 be proper to notice its physical qualities. As far as can be 

 collected from the observations hitherto made, polyhalite is 

 never found with its crystallization of a perfectly regular form 

 but is met with in shapeless masses generally of a compact or 

 lamellated fibrous texture ; yet its fibres, which are parallel and 

 most commonly curved, are so united together that it is hardly 

 possible to distinguish the separate courses of layers. 



Its fracture is irregular and subfestucated {suhfestucaria). 

 The fragments are pointed, and generally edged. Rather indu- 

 rated and brittle. It is somewhat harder than anhydrite, so 

 as to scratch it slightly; while it scratches Iceland spar 

 strongly. It is itself, however, easily scratched by fluor spar. 

 In bnttleness it resembles anhydrite, and may easily be pul- 

 verized. 



In specific gravity it is nearly equal to anhydrite ; for a frag- 

 ment weighing 8*991 grm. in the air lost 2*586 grm. in alcohol 

 whose specific gravity was 0*7964, the mercury in the centigrade 

 thermometer standing at 11*5°, and the barometer 0*748 m. • 

 whence it follows that its specific gravity compared with distilled 

 water is at the above-mentioned temperature and pressure 

 = 2*7689. 



Its colour is a brick-red, which doubtless is to be considered 

 as not natural to this fossil, and to be attributed to the oxide of 

 iron, thoroughly penetrating it, and only mechanically mixed. 



The superficies of the fibrous variety has a pearly lustre, but 

 the compact variety and the fracture of the fibrous possesses a 

 waxen hue. 



With respect to the pellucidity of this fossil, the lesser frag- 



