134 The Monoclinic Pyroxenes of New York State. 



The following faces have thus far been noted on the New York 

 Pyroxenes : 



m (110) OOP «(111)— P 



/(310)qoP3 s(T11)P 



a (100) 00 PS «(221)— 2P 



& (010) OOP do o(221)2P 



c (001) OP ;i('331)3P 



e(Oll)Pa) A(311)3P3^ 



3(021) 2Pa) ,a(121)— 2P2 



p (TOI ) P 5o a ( 312)— |P 3 



Prisms. The unit prism m (110) is a very common face and is 

 almost invariably present. It may or may not exceed the ortho 

 and clino pinacoids in size. The ortho-prism /(SIO) has only 

 been observed on one crystal from this state and that from the 

 Tilly Foster Iron Mine in Putnam Co. It has not been previ- 

 ously recorded from New York State, but is common on many 

 European pyroxenes. 



Pinacoids. The ortho pinacoid a TlOO) and the clino pinacoid 

 b (010) are as common as the unit prisms, but show great varia- 

 tion in their development. When of equal size and greater de- 

 velopment than the prism the section of the crystal is square. A 

 greater development of one of the pinacoids giA'es the crj^stal a 

 tabular habit. Thus the white pyroxenes from Sing Sing, West- 

 chester Co., are nearly always tabular parallel to a while those 

 from St. Lawrence Co. are not uncommonly tabular parallel to 6. 

 The basal pinacoid c (001) is often seen on terminated crystals. 

 A basal parting may give the same appearance to the crystal. 

 The basal pinacoid face is generally rectangular in outline, but 

 this varies somewhat depending on the number of faces which in- 

 tersect it. 



Domes. Two clinodomes and one orthodome occur. The latter 

 is the commonest of the three. It is rarely present without the 

 basal pinacoid and is generally smaller than it. A characteristic 

 exception to this rule is found in the augites from Mt. Adam, 

 Orange Co., and those from the Tilly Foster Iron Mine in Put- 

 nam Co. The two clinodomes e (Oil) and 2: (021) are generally 

 represented by small triangular faces. The dome z is rare, but 

 the dome e is quite a characteristic form on many augites from 

 the Highland Region of Orange Co. 



