Penfield and Ford — Developments of Ccdcite Crystals. 237 



Art. XXIII. — On some Interesting Developments of Calcite 

 Crystals ; by S. L. Penfield and W. E. Ford. 



1. Calcite from Union" Springs, Cayuga County, N. Y. 



The crystals under consideration were found during the 

 summer of 1899 by Mr. J. M. Clarke, Director of the Geo- 

 logical Survey of the State of New York, and were sent to 

 New Haven for examination. Mr. Clarke had observed that 

 the crystals presented certain features of unusual interest, 

 and it was his wish that they should be described and that the 

 specimens should be deposited in the Yale Collection. The 

 crystals occur in the Onondaga limestone, in a region where 

 slight tectonic disturbances have taken place, giving rise to 

 fissures in which calcite has deposited as vein material. The 

 most interesting feature presented by the crystals is their 

 diversity of habit, shown often on a single hand specimen, and 

 due to different methods of twinning together with peculiari- 

 ties in the development of certain crystal faces. 



Most of the crystals were not well adapted for measurement 

 with the reflecting goniometer, but, using one of the smaller 

 ones, about 5 mra in length and 2 mm in diameter, it was possible 

 to identify the prominent forms by means of their angles. The 

 small crystals are quite highly modified and their development 

 is represented by fig. 1. The terminal faces are the brightest 

 and best developed, and are those of the com- 

 mon scalenohedron v, 2131. There was meas- 

 ured for the identification of this form r 

 (cleavage) ^ v, 1011 „ 2131 = 28° 56', calculated 

 29° V 30." In the zone r, v, and making a very 

 small_ angle with v is the scalenohedron v : , 

 7'4r , Il , 3, which is especially prominent on the 

 crystals from this locality. This form was 

 identified by von Bournon on crystals from 

 Derbyshire and the Dauphin e Alps, and appears 

 as form No. 37, plate 31, of his Traite de Min- 

 eralogie, published in 1808. The form was 

 identified by its position in the zone r, v and 

 the measurement v ^ ^=3° 23', calculated 3° 

 55'. On the crystals under consideration the 

 faces of the scalenohedron v x have a vicinal 

 development, and thus the contrast between 

 them and the better developed faces of the 

 scalenohedron v is generally quite marked. A 

 negative rhombohedron, f, truncates the edges of v l and 

 appears always as a narrow face with vicinal development from 

 which no reflection could be obtained. A rhombohedron in this 



