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Xiy. Chemical Examination of, and Remarks on, the Mineral 

 Species Tyrite. Bij D. Forbes, F.G.S., F.C.S., A.I.C.E* 



IN PoggeudorflF's Annalen der Physikund Chemie, 1856, No. 4, 

 p. 622-628, is inserted a communication from M. Kenngott 

 of Vienna, entitled " Notiz liber das Tyrit genannte Mineral," 

 in which the author makes some remarks on the crystalUne form 

 of that mineral, and institutes a comparison between it and the 

 Greenland mineral Fergusonite, from which he concludes that 

 both these species are identical. 



Before making any observations on this question, I am enabled 

 to bring forward a chemical examination of the mineral from the 

 same locality as those examined crystallographically by M. Kenn- 

 gott, and received from Dr. Bondi of Dresden. 



The species is Norwegian, and obtained from the large fel- 

 spar quarry at Helle at Nfeskiil, about ten English miles east of 

 Arendalf, where the mineral occurs pretty abundantly, and occa- 

 sionally in crystals above 2 inches in length. 



These crystals invariably have their bases attached to plates of 

 black mica, and shoot out thence, imbedding themselves in the 

 red orthoclase, which very frequently forms thin plates or slabs 

 of from ^ of an inch to 4 inches in thickness, bounded on both 

 sides by the black mica. 



The annexed woodcut gives an idea 

 of this mode of occurrence. 



The minerals associated are orthite, 

 alvite,ametallic mineral containingura- 

 nium, uranium ochre, and a new mine- 

 ral of abrown-red colour not yet analysed. 



In none of the very numerous crystals I have obtained are the 

 angles otherwise than extremely uneven and indistinct, having 

 often a rounded or compressed appearance, and are almost always 

 pyramidal, running off to a point without any distinct facets. 

 Not the slightest degree of reliance could be put upon measure- 

 ments obtained by the hand-goniometer. They present a qua- 

 drilateral section, and are probably tetragonal, having one distinct 

 cleavage plane, and traces of two others. The fracture, cleavage, 

 and colour are so different from those of the original Tyrite from 

 Hampemyr on Tromoe, that, until after the present analysis was 

 made, it was considered uncertain whether they were the same 

 mineral. 



* Communicated by the Author. 



t There is a mistake in the locality as given by M. Kenngott ; Helle being 

 on the mainland at Na'skiil, and not on the Island of Tromoe. A section 

 of this quarry will be found in the Quarterly Journal of the Geological 

 Society of London, May \H!J3. . Dr. liondi's specimens were, 1 believe, 

 collected by Zscbau of Dresden. 



