the identity of Zeagonite and Phillipsite, S,-c. Ill 



translucent ; those in the black part are black and opaque, 

 and probably coloured by the same kind of matter as colours 

 the matrix. Hence the analysis of the black crystals, which 

 are the only ones yet analysed, must fail to give the true con- 

 stituents of the mineral, and the theoretical chemical formula 

 must be incorrect. The crystals are similar in form to the 

 small single crystals of felspar coated with chlorite, which are 

 brought from St. Gothard. 



Pseudomoi-phous Crystals from a Mine at Haytor^ in Devonshire. 



In the year 1827 some crystals were found in this mine, 

 which were described by Mr. W. Phillips and Mr. Levy, under 

 the name of Haytorite*. It was obvious that the substance of 

 the crystals was calcedony ; and as they nearly agreed in form 

 and angular measurement with Humboldtite, it was supposed 

 they might have derived their pseudomorphous character 

 from crystals of that substance, although from the solidity and 

 state of aggregation of some of the crystals which were first 

 discovered, it was difficult to imagine the mode by which the 

 borrowed forms could have been produced. It is, however, 

 equally difficult to comprehend the manner in which the well- 

 known pseudomorphous crystals of steatite, imbedded in the 

 same substance, could have been produced. These present 

 the forms of quartz and of carbonate of lime, and they con- 

 sist of steatite apparently homogeneous with the mass in which 

 they are imbedded. We might indeed suppose that a cavity 

 partly occupied by crystals of quartz and carbonate of lime 

 had been filled by steatite ; that subsequently the quartz and 

 carbonate of lime had disappeared and left moulds which were 

 afterwards filled by the same /«m(Z of steatite. But it is not easy 

 to conjecture how the mould and the casts formed at very dif- 

 ferent times should be homogeneous. With regard, however, to 

 Haytorite, there cannot now exist a doubt of its pseudomorphous 

 character ; many of its crystals being hollow, sometimes very 

 thin, and the inner surfaces mammillated like ordinary calce- 

 dony. I have also a crystal of this substance which presents 

 a form analogous to the common hemitrope crystals of sphene 

 from St. Gothaid, with a deep re-entering angle, and evi- 

 dently formed within a polished cavity which it has onl}' par- 

 tially filled. But in addition to the evidences of pseudomor- 

 phism presented by many of the crystals of Haytorite, there 

 have been found in the same mine other pseudomorphous 

 crystals representing several of the forms of carbonate of lime, 

 some of which are solid, and some hollow: among these are 



• See Phil. Mag. and Annals, N.S. vol. i. p. .38, 40, 43.— Kuir. 



groups 



