164 The Monoclinic Pyroxenes of New York State. 



abundance. These are almost invariablj' of the same habit, with 

 a strong flattening parallel to the orthopinacoid. The^^ occur as 

 single individuals in zones or sometimes as Mr. F. L. Nason in- 

 forms me, in rounded masses. The crystals ai'e colorless to 

 milkwhite and translucent to opaque. They might, perhaps, be 

 classed with the diopsides judging from the appearance of some, 

 but the higher percentage of alumina classes them with augite, 

 and it seems to the writer that the varietj^ name of Leucaugite 

 may be appropriately applied to them. 



Sing Sing, Westchester Co. — The usual combination of forms 

 is a (100), & (010), m (110), t; (221), and o(221)(Pl. XY, Fig. 4) 

 less commonly c (001); p (101) is very rare and was not&d on 

 one specimen in the collection of Columbia University, w(lll) 

 is equally rare. In rare cases a (100) and 6(010) are wanting or 

 are very narrow, so that the cr3^stal has a square appearance. 

 One specimen in the same collection shows v (221) but not o (221), 

 (PL XY, Fig. 2.) 



A strong basal and orthopinacoidal parting, both due to twin- 

 ning are present, but the latter is rare. The crj^stals are fre- 

 quently superficially altered, to tremolite, and nearly all are 

 stained exteriorly with limonite. The prison quarry has yielded 

 the best specimens in former years, but ver}^ few are found now. 

 There is a granite dike cutting the limestone a few hundred feet 

 south of the quarry, but there is no evidence to show that the 

 cr^'-stals are the result of contact action. 



An analysis was made of some nearly transparent pieces of a 

 crystal from Sing Sing, with the following results : 



Percentage. 



SiO^ 53.30 



FeO 80 



CaO 24.82 



MgO 16.18 



AI2O3 4.11 



H2O 15 



99.36 



Sp. Gr. 3.18, Ries. 

 3.10, Beck. 



The above calculated gives Ca4oMg36FeiAl8Si8o0249 or ap- 

 proximately. 



Ratio. 



Prop, parts. 



.8883 



80 



.0111 



1 



.4432 



40 



.4045 



36 



.0401 



4 



