i86 



NEW YORK STATE MUSEUM 



LETTER 



ANGLE 



MEASURED 



CALCULATED 



a : t 



100 : II .3.0 



r 21' • 



-0 tQI' 



/ I02 



: m 



: no 



25 12 



25 io| 



: ^ 



: 120 



43 17 



43 13I 



: g 



:370 



47 15 



47 39^ 



: r 



: 130 



54 44 



54 39I 



: h 



: oip 90 2 



90 



PYROXENE FROM JEROME PARK RESERVOIR 



The material upon which the following note is based was collected 

 in November 1904 by Mr J. H. Adams, from an excavation at the 

 southern end of the Jerome Park Reservoir at Jerome avenue and 

 205th to 207th streets. A suite of twelve specimens from this find 

 v\^as placed at the writer's disposal for study, through the courtesy 

 of the American Museum of Natural History of New York City, 

 which institution is now the repository of the type specimens. 



The minerals occur in a limestone vein in Fordham gneiss, the 

 point of contact being marked by titanite, brownish-green actinolite 

 in flat acicular crystals, albite and pyroxene. The last mineral which 

 occurred on two of the specimens studied consisted of small crystals, 

 the largest measuring 20 mm in length and 2x5 mm 

 in cross section, which marked the contact phase, 

 and minute crystals averaging i mm in diameter, 

 occurring embedded in the calcite of the vein. The 

 largest crystal of the group is shown in figures 6a 

 and 6b. The forms observed on this crystal are : 

 c(ooi), fc(o'io), 0(100), /(310), m(iio), i{iZ0), 

 £'(011), l|(o3i)*,^(ii2), //(121), /?(l32), ^^(721), 

 0(211), and I (321)*. 



The forms marked with an asterisk (*) are new 

 to the species. In habit this crystal is characterized 

 by the prominence and brilliancy of the planes of 

 the pyramid ^(112), a comparatively rare form for 

 pyroxene. The new clinodome |)(o3i) was observed 

 only once on this crystal, partly due to the fact that only one termina- 

 tion was exposed. The face noted, however, gave a fair image of the 

 signal, fell well in zone with the basal and clinopinacoids and showed 

 a close correspondence between measured and calculated angles. The 

 new pyramid 1(321) was observed from one well-developed plane 



Fig. 6 



