282 Mr Haidinger on the Parasitic Formation of Minerals, 



geodes of brown hematite, that is, of prismatic iron-ore. Hiit- 

 tenberg in Carinthia has perhaps no equal in illustrating the 

 exactness of this explanation, for the distinctness of the speci- 

 mens which it affords. The geodes occurring at that place, 

 of various sizes, are very frequently adorned with crystals of 

 Arragonite, of calcareous spar, of prismatic manganese-ore, 

 or with the silvery flakes of another manganesian mineral, 

 whose exact chemical composition has not yet been ascertained. 

 With the decomposition of the sparry iron is also intimately 

 connected the formation of those beautiful coralloidal varieties 

 of Arragonite known by the name of Jbs Jerri, which are 

 found in caverns near the surface of the rocks, as at Eisenerz 

 in Stiria. 



The Ankerite, or paratomous lime-hahide of Mohs, is also 

 apt to be decomposed in a similar manner. But as it is a 

 compound of the carbonates of lime and iron, in which the 

 former amounts to more than half the weight, only what might 

 be termed a skeleton of the hydrate of iron remains, while the 

 rest of the ingredients disappear by the action of chemical 

 agents. The texture of the remaining mass is much less com- 

 pact than that of the residue left by the decomposition of the 

 sparry iron. 



The product of the decomposition of the two species last 

 mentioned is exactly the same as the substance which remains, 

 when iron-pyrites suffers a decomposition, without changing its 

 form. Both species, the hexahedral and the prismatic iron- 

 pyrites, having the same mixture, are also subject to the same 

 change : the sulphur goes away, and the iron takes up oxygen 

 and water ; the decomposition proceeds from the surface. We 

 often see crystal^ covered on the surface with a brown tarnish, 

 and this is the first stage of the change. There are specimens 

 with a thin coat of the hydrate of iron ; there are others con- 

 sisting almost entirely of the latter, with only a nucleus left of 

 the original bisulphuret of iron. Such are found at Wochein 

 in Carniola, where this hydrate of peroxide of iron, produced 

 from the decomposition of the bisulphuret, occurs in such 

 abundance and pureness, that it is melted as a very valuable 

 ore of iron. The iron extracted from it is particularly re- 

 markable for its softness. 



