FELDSPAIt GROUP. 



279 



Moonstone is an opalescent variety of adularia, having 

 when polished peculiar pearly reflections. Sunstone is simi- 

 lar; but contains minute scales of mica. Aventurine feld- 



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spar often owes its iridescence to minute crystals of specular 

 or titanic iron, or limonite. Sunstone and moonstone are 

 mostly oligoclase, and so is a large part of aventurine feld- 

 spar. 



Diff. Distinguished from the other feldspars by its right- 

 angled cleavage and the absence of striated surfaces. 



Obs. Orthoclase is one of the constituents of granite, sye- 

 nyte, gneiss, and other related rocks ; also of porphyry, and 

 trachyte ; and it often occurs in these rocks in imbedded 

 crystals. St. Lawrence County, N. Y., affords fine crystals ; 

 also Orange County, N. Y. ; Haddam and Middletown, 

 Conn. ; Acworth, N. H. ; South Royals ton and Barre, 

 Mass., besides numerous other localities. Green feldspar 

 occurs at Mount Desert, Me.; an aventurine feldspar at 

 Leiperville, Penn. ; adularia at Haddam and Norwich, 

 Conn., and Parsonsfield, Me. A fetid feldspar (sometimes 

 called necronite) is found at Roger's Rock, Essex County ; 

 at Thomson's quarry, near 190th Street, New York City, 

 and 21 miles from Baltimore. Carlsbad and Elbogen in Bo- 

 hemia, Baveno in Piedmont, St. Gothard, Arendal in Nor- 

 way, Land's End, and the Mourne Mountains, Ireland, are 

 some of the more interesting foreign localities. 



