of Mineral Species. Ill 



this way from the surrounding mass, terminated on both ends, 

 and altogether shewing only a small portion of its surface, where 

 it might have been attached to an original support. 



In the example just now described, the crystals of quartz are 

 deposited pretty regularly, at least in so far as their axes are 

 nearly perpendicular to the surface of the crystals of calcareous 

 spar. This is not the case in the prismatoidal manganese-ore 

 from Ihlefeld, which fills up, and at the same time surrounds, 

 the space formerly containing crystals of calcareous spar, and 

 where likewise nothing but the surface of the original crystals 

 has remained. Both masses, however, are perfectly alike, and 

 consist of granular individuals, still easily recognizable. Such 

 component individuals are sufficiently small to withdraw them- 

 selves from observation, in the varieties of compact rhombohe- 

 dral iron-ore from Johanngeorgenstadt in Saxony, and other 

 places, which exactly, like the manganese-ore, include shapes, or 

 rather surfaces of crystals only, of calcareous spar. 



A similar explanation no doubt applies also to the steatite 

 from Goepfersgriin in Bayreuth, well known to collectors, but as 

 to the causes which have produced it, still unknown to minera- 

 logists. Their perfectly homogeneous appearance excludes every 

 idea of their being formed by a mixture, however intimate, of 

 steatite, and the species whose forms the crystalline shapes af- 

 fect ; 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 species, as quartz, 

 calcareous spar, and pearl-spar, likewise distinctly 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 



