NuttalPs Geological and Mineralogkal Remarks. 245 



pscudo productions of the Missouri, have yet, however, 

 been discovered" in the territories of the United States. 



The cOiVDROi>iTK, orBRuciTE, almoat peculiar to Spar- 

 ta, discovered likewise by the celebrated Berzelius, in Fin- 

 land, accompanied by gray Spinelle, is (according to an un- 

 published analysis which J made in 1820,) a silicate of 

 magnesia with an accidental portion of fluoiic acid and 

 iron. The same result has been obtained by Dr» Torrey, 

 from whom I copy the following description of its crystal- 

 lization* Jt occurs occasionally in small four-sided prisms, 

 (of a paler colour than the amorphous masses.) with rhom- 

 bic bases of 124"^ and 56° truncated on the acute lateral 

 edges by planes which form with the contiguous sides of 

 the prism angles of 122^ and 1 ] 4° The prism is tormina- 



I 



ted by dihedral summits whose faces meet under an obtuse 

 angle, and correspond to the acute, truncated edges of the. 

 prism. The edges of the summits are oblique to the axis 

 of the prism, but not parallel to each other ; or they may 

 be said to be alternately oblique at each extremity." 



Ilaiiy, also, by cleavage, had obtained from it a rhom- 

 boidal prism ; andBerzelius, w^ho then compared it analyti- 

 cally w^ith his condrodite, concluded it to be identic. The 

 former, with his usual sagacity, referred it to his peridot/ 

 as it does not indeed very materially dijfTer in composition 

 from olivin or amorphous chrysolite: still the crystalliza- 

 tion proves it to be a very distinct species. It is of a 

 bright browmish yellow, bordering on orange, disseminated 

 'n masses commonly about the size of a hazle nut, exhibit- 

 ing more or less of the rhombic form, throughout a white 

 and fohated lime-stone, generally containing scattered 

 hexagonal lamlns of plumbago, and more rarely, bluish 

 pellucid crystals of phosphate of Hme. It is imperfectly 

 lamellar in one direction, splintery in the other, with a glas- 

 sy or almost resinous lustre, the fragments either translu- 

 cent or nearly opaque, and sufficiently hard to scratch glass. 

 Before the blowpipe it is infusible, but with borax forms a 

 glass, though not very readily. Its gravity is a sniall frac- 

 tion above 3. 



Throughout the valley of Sparta the condrodite is by no 

 means uncommon, but variable in its appearance* Th^' 

 finest and clearest masses are obtained at the town of Spar- 

 ta. Though abundant at Franklin, it is here opaque and 

 of a deeper tinge of colour. It occurs thickly dissean'nu- 



32 



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