1*74 The Monoclinic Pyroxenes of New York State. 



bination of forms : a (100), 6 (010), c (001) (PL I, Fig. 4); h (010), 

 m(llO), c(OOl) (PI. I, Fig. 3); a (100), 6(010), m (110), c (001) 

 and ri(lll), similar to form from Gouverneur shown in PI. IV, 

 Fig. 4. 



Nearly all of the individuals show a strong basal parting, due 

 to twinning. Uralitization is probably better developed in these 

 crystals than those from any other locality in the State. All 

 stages of transition can be seen from the pyroxene crystal, whose 

 faces present a slightly fibrous appearance, to one whose 

 whole mass has been converted into fibrous amphibole. Some- 

 times the crystals are cracked apart and the separated portions 

 held together by amphibole fibres. Penetrations of one diopside 

 crystal into another are not uncommon. One crystal from this 

 locality in the Root collection at Hamilton College is 4x4x12 

 inches in size. Another in the Columbia University collection 

 had a small, perfectly formed crystal of mica similarly oriented 

 included in it. 



The green glassy crystals are all of simple prismatic habit, and 

 show only the forms a (100), &(010), m(llO). They are termi- 

 nated bj'- parting planes parallel to the base. The faces of the 

 prismatic zone sometimes show traces of uralitization, but de- 

 composition takes place usually along the parting planes, result- 

 ing in powdery alteration product, probably serpentine. Twinning 

 parallel to a (100) and c (001) is seen in nearly every specimen,, 

 and a strong prismatic cleavage is frequent. 



The following analysis shows the composition of this green 

 glassj^ diopside. 



Percentage. Ratio. Prop, parts 



SiO,, 54.94 .9156 50 



FeO 1.29 .0179 1 



CaO 25.38 .4156 23 



MgO 17.60 .4400 24 



AlA 2.42 .0236 1 



Alkalies 28 



99.91 



= MgtCa3FeiAl.,Si5oO,5i 

 or Mg Alj SiOfi 

 Fe Ca SiaOfi 

 22 (Ca Mg Si A) 

 Sp. Gr. 300. 



