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NEW YORK STATE MUSEUM 



rendered difficult, and where fairly sharp reflections were obtained 

 from the corresponding faces of a number of crystals, the results 

 showed a considerable variation, probably due to incipient groupings 

 of a number of crystals in approximately parallel position. The 

 brachi dome r (014) was noted in a number of cases but always 

 trending toward a connection with (011) and (001) by series of 

 vicinal planes giving curved surfaces [fig. 2]. Twinning parallel 

 to (no) is quite common producing the usual stellate forms. In 

 one case the repeated twinning shown in figure 2 was noted. Ag- 

 gregates of the usual "cockscomb" aspect are common. 



Pyrite. The pyrite which occurs at Rondout presents several 

 features of interest both from a crystallographic and a genetic 

 point of view. In addition to the small brilliant crystals (1 milli- 

 meter diameter) which in places thickly incrust the calcite of this 

 locality, in a number of specimens a decided and unusual distorted 

 habit was noticed in the pyrite crystals occurring associated with 

 the dolomite, whi.ch latter appeared to be of a younger generation 

 than the calcite. The distortion takes place perpendicular to the 

 opposite faces of a cube (100) and varies in extent from an elonga- 

 tion of five times the cross section to thin acicular crystals some- 

 what resembling the acicular habit of millerite. Twinning occurs 

 parallel to the dodecahedral (no) face [fig. 3], giving rise to L and 

 T shaped crystals. Repeated twinning occurs in several cases. 

 Scepter crystals resembling those common to quartz were observed 

 in several instances, the relation between the acicular shaft and 

 the crowning individual being that shown in figure 4. Pyrite 

 dendrites of remarkable size and beauty occur in seams in the 

 limestone. These bear a marked resemblance to the arborescent 

 forms of native copper and may owe their origin to similar crys- 

 tallographic development. 



Quartz. Crystallized quartz is found at Rondout for the most 

 part in detached crystals contained in the clay pockets of the 

 Manlius limestone which forms the hanging wall of the cement 

 beds. These exhibit in a great number of instances the phenome- 

 non of a clearly marked inner crystal of smoky quartz surrounded 

 by a secondary layer of colorless quartz. These phantoms of 

 smoky quartz occasionally occur in series showing successive de- 

 posits of smoky and clear quartz. Small amounts of anthracite 

 were noted in the associated limestone. In many of the crystals 

 a marked tendency toward parallel grouping, very similar to the 

 occurrence of quartz at New Baltimore 1 , often results in cavernous 

 crystals which closely resemble those from Stony Point, N. C. 



>N. Y. State Mus. Bui. 58, pi. 1. 



