314f Mr. Rose on Felspar and other Crystals. 



solid mass of perpetual ice. It is about ten miles in breadth; 

 its length (of course not having been traversed) uncertain. 

 The ebb tide is from the south-west, and the flood from 

 south-east; small channels ran through it, but not wide 

 enough to work a ship. 



ON FELSPAR, AL13ITE, LABRADORE SPAR, AND ANORTHITE. BY 

 GUSTAVUS ROSE, OF BERLIN. 



Some differences which Mr. Rose observed in the angles of 

 certain crj'stals, hitherto classed among the felspars, led him 

 to make a closer investigation of them ; the result of which 

 was, that under these crystals are contained four species, dif- 

 fering both in a crystallographical and chemical point of view, 

 though in the former respect they exhibit an undoubted ana- 

 logy- 

 Felspar proper, KS^ + 3AS', is the most abundant of these 

 species. To it belong the Adularia of St. Gothard, the glassy 

 felspar of Vesuvius and the Siebengebirge, the Amazon-stone 

 of Siberia, the Labradore felspar from Friedrichswarn in Nor- 

 way, the felspar of Baveno, Carlsbad, and the Fichtelgebirge, 

 and generally most part of Werner's common felspars. 



The second species, Albite, is more rare. It is denoted by 

 NS^ + SAS^. Eggerts first found it in an uncrystallized fi- 

 brous and granular form at Finnbo and Broddbo, near Fah- 

 lun, and thereafter Haussmann and Stromeyer in a mineral 

 from Chesterfield, in North America, to which the former gave 

 the name of Kiefelspath. Nordenskiold found it in a granite 

 at Kimite, near Pargas, in Finland ; and Ficinus in a granite 

 from Penig in Saxony. All these are uncrystallized varieties. 

 To the crystallized, which I have had occasion to see, belong 

 the white schorl, first described by Rome de ITsle; the fel- 

 spar crystals of Dauphiny of Haliy ; the small crystals from 

 Saltsburg and the Tyrol, known a few years ago under the 

 name of Ad ularia. 



The third species forms the Labradore spar, which Klaproth 

 analysed and distinguished from felspar, though mineralo- 

 gists did not consider it as a distinct species. Berzelius has 

 assigned to it the formula NS'^ + S CS^-|-12 AS from Klaproth's 

 analysis. 



The fourth species is the rarest of the whole. Mr. Rose has 

 recognised it only in the druses of limestone blocks, which are 

 found at Mount Somma, near Vesuvius, where it occui's in 

 small shining perfect crystals. He has detei'mined its formula 

 to be MS+2 CS-:-8 AS ; and has called it Anorthite. 



Albite is readily distinguishable by the twin grouping of its 

 crystals. Its primitive form is an irregular parallelopiped. 



In 



