94> Mr Haidinger on the Parasitic Formation of Minerals^ 



include shapes, or rather surfaces of crystals only, of calcare- 

 ous spar. 



A similar explanation no doubt applies also to the steatite 

 from Goepfcrsgriin in Bayreuth, well known to collectors, but 

 as to the causes which have produced it, still unknown to mi- 

 neralogists. Their perfectly homogeneous appearance excludes 

 every idea of their being formed by a mixture, however inti- 

 mate, of steatite, and the species whose forms the crystalline 

 shapes* affect; for, on this supposition, they still must retain 

 some of the properties peculiar to those species. The fact that 

 several forms are found, not only incompatible with each other, 

 but evidently belonging to other two or more well known spe- 

 cies, as quartz, calcareous spar, and pearl-spar, likewise dis- 

 tinctly proves them not to be actual crystals, belonging to the 

 internal nature of steatite. But if we compare the analogy of 

 such bodies as those described above, which, like the steatite, 

 include only the form of another species, we can have no doubt 

 that all of them must have been formed in the same way. 

 The chemical composition of steatite is not well ascertained : it 

 is probably a compound of some silicate and of a hydrate of 

 magnesia. Quartz is entirely composed of one of its ingredi- 

 ents ; 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 crystals have been replaced by steatite, do not contain so much 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 without giving up part 

 of their ingredients to the new mixture, while the latter was 

 forming within and without the space which these crystals oc- 

 cupied. 



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 Transyl- 

 vania, considered by Werner as crystallized green-earth, by 

 Hauy as a variety of steatite ; the red masses sometimes show- 

 ing 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 

 decomposition of the porcelain-spar of Fuchs ; {Denl^schriften 



