112 Mr HAIDINGER on the Parasitic Formation 



is not well ascertained : it is probably a compound of some sili- 

 cate and of a hydrate of magnesia. Quartz is entirely composed 

 of one of its ingredients ; but the other species, calcareous spar, 

 for instance, whose crystals have been replaced by steatite, do 

 not contain so much as a trace of these substances, so that we 

 must suppose them to have been entirely destroyed, even with- 

 out giving up part of their ingredients to the new mixture, while 

 the latter was forming within and without' the space which these 

 crystals occupied. 



Earthy and friable masses are often the result of decomposi- 

 tion, that is to say, of a change in the arrangement of particles, 

 which then are so minute, that none of their natural-historical 

 properties can be ascertained. The pale green friable masses, 

 in the form of crystals of pyroxene, from Tyrol and Transylva- 

 nia, considered by WERNER as crystallized green-earth, by HAUY 

 as a variety of steatite ; the red masses sometimes shewing the 

 forms of olivine, and dependent upon the decomposition of that 

 species, included in some of the rocks of Arthur's Seat, near 

 Edinburgh ; porcelain-earth, probably owing to the decompo- 

 sition of the porcelain-spar of FUCHS * ; various kinds of stea- 

 tite, quoted by authors, some in the form of garnet, others 

 in the form of trigonal-dodecahedrons of an unknown mineral, 

 engaged in the serpentine from Sjberia, others in the form of fel- 

 spar, &c. yield examples of such bodies. They have not yet been 

 examined with that degree of attention which they deserve, not 

 so much perhaps on their own account, as rather for the infe- 

 rences to which researches of this kind might lead. But it must 

 be allowed, that many of them cannot be instituted in those 

 fragments of the entire series, which, for their more apparent 

 distinctness, are preserved in our mineralogical cabinets. Beside 



* Denkschriften der Akademie der Wissenschaften zu Milnchen fur 1818 und. 

 1819. 





