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Experiments on a Mineral Substance formerly supposed to be Zeolite ; 

 with some Remarks on two Species of Uran-glimmer. By the Rev. 

 William Gregor. Communicated by Charles Hatchett, Esq. F.R.S. 

 Read July 4, 1805. [Phil. Trans. 1805, p. 331.] 



The mineral substance treated of in this paper, is similar to that 

 of which Mr. Davy, some months ago, gave an account, under the 

 title of Hydrargyllite or Wavellite. That which is now described by 

 Mr. Gregor is produced from a mine called Stenra Gwyn, in the 

 county of Cornwall. 



Two species of this substance, the author says, are found in the 

 above-mentioned mine ; the first, and most common, consists of an 

 assemblage of minute and delicate crystals, in radiated tufts, attached 

 to quartz crystals. These crystals are in general white and trans- 

 parent; sometimes, however, they have a yellowish hue. They vary 

 considerably in their size, but seldom exceed a quarter of an inch in 

 length. 



Among these crystals are frequently seen two kinds of crystalline 

 laminae ; one of them being in the form of parallelopipedons, with 

 truncated angles, and of a green colour ; the other forming an as- 

 semblage of square plates, varying in thickness, and the angles of 

 which are not always coincident ; these are of a bright wax yellow. 

 This last kind is also found adhering to the sides of quartz crystals, 

 in the cavities of granite. 



The other species of the substance here treated of, consists of 

 crystals closely compacted together in the form of mammillary pro- 

 tuberances, generally of the size of small peas, and forming a stratum 

 about one eighth of an inch thick, upon quartz, in the cavities or 

 fissures of compact granite. The striae of these mammillae diverge 

 from a centre, like zeolite. 



The detached crystals of the first species are easily reduced to powder. 

 Their specific gravity, at 56 Fahr., was found to be 2- 22. The se- 

 cond, or more compact species, is sufficiently hard to scratch calca- 

 reous spar : its specific gravity, at the temperature of 55, was 2 '25 3. 



The crystals of the first species, when suddenly exposed to the 

 action of the blowpipe, decrepitate ; if gradually exposed to its ac- 

 tion, they grow opake, but show no signs of fusion, even under the 

 strongest heat. Both species, when exposed for some time to a red 

 heat, experience a diminution in weight of about 30 per cent. 



Some other experiments upon these substances are related, and a 

 very minute account of the mode in which they were analysed is 

 given ; of this we must necessarily confine ourselves to give merely 

 the results. 



Fifty grains of the crystals of the first species yielded alumina 

 29-H- grs. ; silica, 3 T V grs. ; oxide of iron, T V grs. ; lime, W grs. ; 

 volatilized matter, 14$ grs. 



The sum total of these is 47-A- grs. 



Consequently the loss was 24-g- grs. 



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