FELDSPAR 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- 

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 
erystals. St. Lawrence County, N. Y., affords fine crystals ; 
also Orange County, N. Y.; Haddam and Middletown, 
Conn.; Acworth, N. H.; South Royalston 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 196th 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, 
