106 Mr HAIDINGER on the Parasitic Formation 



of zinc or magnesia by heat, as described above. The other hy- 

 pothesis, that the lime in the original species has been subse- 

 quently replaced by the oxides of iron and manganese, is ren- 

 dered more likely by the fact, that there are crystals which in 

 part consist of the scheelium-baryte, while near the surface, but 

 within the planes of the original crystals, and where portions of 

 them seem to be wanting, we observe an aggregate of crystals of 

 the scheelium-ore. A specimen of this kind I saw at Schlaggen- 

 wald, its native place. 



Here we must also consider Haytorite, a substance newly 

 discovered, but which has already given rise to various and con- 

 tradictory hypotheses, and in connection with it some of the 

 pseudomorphoses of rhombohedral quartz in general. Haytorite 

 has been ascertained by Mr LEVY to have the shape of the spe- 

 cies to which he gives the name of Humboldtite. All those mi- 

 neralogists who have examined it, agree in pronouncing the sub- 

 stance of it to be calcedony, which is itself a granular compound of 

 exceedingly minute individuals of rhombohedral quartz : so much 

 appears from its physical characters. Dr BREWSTER obtained 

 the same result, by ascertaining its action on light. He has also 

 directed the attention of naturalists to the circumstance, that 

 the planes of composition between the different individuals, and 

 which are always so very distinct in datolite, are as distinct as 

 possible in haytorite ; and hence he draws the correct inference, 

 that they cannot have been formed in a mould, like the pseu- 

 domorphoses. Datolite contains a notable quantity of silica, 

 36.5 per cent, according to KLAPROTH'S analysis. The succes- 

 sive exchange of its contents of lime and boracic acid for an ad- 

 ditional quantity of silica, if it goes so far as completely to de- 

 stroy the original species, will transform the substance of the 

 crystals into a mass of calcedony. There is no proof, however, 

 that such a process has actually taken place, so long as we do 

 not discover the remains of the former species included in the 



