488 A. J. Moses — Mineralogical Notes. 



Art. LVIII. — Mineralogical Notes; by Alfred J. Moses. 



1. JPyrite Crystals from Kings Bridge, JV. Y. 



The crystals described in this paper were obtained on 

 November 19, 1892, by G. F. Sherman and E. H. Messiter, 

 students of the Columbia College School of Mines, from mate- 

 rial recently quarried within 300 feet of the eastern end of the 

 cut known as "the Harlem River Improvement" at Kings 

 Bridge, ISTew York City. The pyrite crystals were in a nar- 

 row cavity, in a block of limestone, associated with small 

 crystals of dolomite, very pretty crystals of pale green trans- 

 parent mica and curiously modified crystals of quartz. In a 

 few instances minute crystals of rutile were also noticed. 



The pyrite crystals are rarely more than \ inch in their 

 longest dimension but a few were found almost \ inch in 

 length. In most of the crystals the prevailing form is the 

 octahedron always however modified by three or more other 

 forms. The curious fact was noticed that in all the specimens 

 showing quartz the general shape of the pyrite crystals was 

 cubic and the crystals were relatively small. No large crystals 

 of the cubic type were observed. 



The angles were measured with a Mallard- Wollaston goni- 

 ometer reading to half minutes. The angles obtained were : 





Measured. 



Calcui 



iated. 



W-2 



39° 13!' 



39° 



16' 



1/vS-l 



22° 14!' 



22° 



15' 



1^2-2 



19° 25!' 



19° 



28' 



KU2-2 



35° 19' 



35° 



16' 



i- 2 A 8-| 



16° 59' 



17° 



H 



Closer results might have been obtained by readjustment but 

 these were sufficiently exact to determine the symbols beyond 

 question. 



The occurring faces (see fig. 1) are therefore the common 

 faces of pyrite : cube (100, i-i) ; octahedron (111, 1) ; and pen- 

 tagonal dodecahedron (120, i-2) ; and the rarer forms : diploid 

 (321, 3-f) and tetragonal trisoctahedron (211, 2-2). 



In pyrite crystals striations are frequently found upon the 

 faces of the cube and pyritohedron (i-2) parallel to the inter- 

 sections of the faces of these forms and this is attributed to 

 oscillations between the two forms. In the crystals from 

 Kings Bridge all faces except those of the cube are more or 

 less striated sometimes with only one or two very prominent 

 lines, at other times in several directions and with many lines. 



