ON SPURIOUS CRYSTALS. gy 



equivocal. The fluate of lime, sulpliate of barytes, and car- 

 bonntc of lime, which are found in the same places, are so 

 many faithful witnesses, which point out the source whence 

 these forms are derived : and though we are not able to ex- 

 plain completely every circumstance respecting them, their 

 nature cannot be doubted. When we find steatite exhibiting Steatite, 

 itself under several of the forms of carbonate of lime, may 

 we not with great probability infer, that it has only imitated 

 (juartz by deriving from the same source the forms common 

 to both? and when it presents itself under the forms that be- 

 long to quartz, is it not highly probable, that these forms are 

 no more peculiar to it, than those of carbonate of lime are to 

 quartz i" 



But it may be said, the crystals of steatite so perfectly re- 

 semble the mass in which they are enveloped, that we must 

 suppose them to be the same substance, differing only in re- 

 gularity of form. To this I would answer, such an inference Crystals do not 



is contradicted by analogy: for, when a substance is re^u- fo'^common- 

 •'='•'' ^ ly m a muss of 



larly crystallized, and its crystals are enveloped in an amor- the same sub- 



phous mass serving as their matrix, this is commonly of a ^^^"^^' 

 different nature. Thus fine limpid crystals of hyaline quartz Instances, 

 with two points are found buried in white Parian marble, in 

 certain clays or marles, and in porphyries; crystals of hema- 

 toid quartz, or red jasper, and of borat of magnesia, are con- 

 cealed in masses of gypsum ; crystals of sulphate of lime are 

 commonly found in banks of clay; crystals of specular iron 

 ore, garnet, tourmalin, and magnesian limestone, occur in 

 micaceous schist; &c. 



It may be said farther, that the steatite, which exhibits Steatite in a 

 forms analogous to those of rock crystal, presents others, that Peculiar form: 

 appear to be peculiar to itself; such for instance as the hex- 

 agonal prism with hexaedral pyramids truncated on the edges 

 contiguous to the summit, which raises the number of termi- 

 nal faces to twelve. This observation, I confess, might have but this has 

 been adduced as a very plausible objection, before quartz had ^'"^^ ^^^ 



If these pseudomorphoses of our departments be compared with these 

 of Saxony, Bohemia, and Hungary, described by baron von Born, we 

 shall find, that they present ihe same circumstances of form and situation, 

 ind have a similar origin. 



Vol. XX.— June, 1808. H shown 



