226 . Pen field and Ford — Calaverite. 



Since the publication of Dr. Hillebrand's paper it has always 

 been the intention to again take up the study of the crystalli- 

 zation of calaverite, and requests have been made to numerous 

 friends to secure, if possible, material suitable for study. 

 These requests have been generously responded to, and we 

 take special pleasure in here expressing our obligations to 

 Messrs. Lazard Calm of New York, T. A. Rickard of Denver,' 

 and Maynard Bixby of Salt Lake City, for the pains which 

 they have taken to secure the materials needed for the present 

 investigation. In addition to the materials sent us by the 

 gentlemen whose names have just been given, we have also 

 the crystals furnished by Dr. Hillebrand, already referred to. 

 Altogether we have been able to include in our investigation 

 crystals from five different mines in the Cripple Creek region. 



The results of the present investigation indicate that cala- 

 verite crystallizes in the Monoclinic System. The crystals are 

 prismatic or lath-shaped, with their longer axes corresponding 

 to the ortho- or symmetry-axis b. The development of the 

 crystals thus corresponds to that commonly observed on epi- 

 dote. Invariably, as observed by us, the crystals are striated 

 parallel to their longer direction, due to oscillatory combina- 

 tions of the forms in the ortho-dome zone. The oscillations 

 generally give rise to a rounding of the edges in the striated 

 zone, and often very irregular cross-sections result therefrom, 

 as will be shown. When this prominent zone is studied with 

 the reflection goniometer, there often results an almost unbroken 

 succession of reflections of the signal as a crystal is turned. 

 There is no especially prominent face in the zone which may 

 be easily identified, and relied upon as a starting point in mak- 

 ing a series of measurements, Terminal faces, on the other 

 hand, are generally free from striations and are in every way 

 satisfactory for measurement with the reflection goniometer. 

 Uncertain or multiple reflections of the signal, due to vicinal 

 development of the faces or other disturbing causes, were sel- 

 dom encountered. All of the work of determining the system 

 of crystallization, the axial ratio and the symbols of the forms 

 had to be based upon measurements made from the terminal 

 faces, and these being at times unequally developed, and 

 always quite small, the problem proved to be an unusually 

 difficult one. It may not be out of place to state at this point 

 that in the unequal development of the crystal faces, in the 

 scarcity of zones, and in the complex symbols derived from 

 the measurements, calaverite crystals are unlike any that have 

 ever come to the attention of the present writers. The crys- 

 tals seem almost to present a contradiction to some of the laws 

 of crystallography. 



Determination of the Axial Ratio. — The crystal which 



