90 



J. E. Pogue — Cerussite Twin. 



Art. X. — On a Cerussite Twin from the Mammoth Mine, 

 Pinal County, Arizona ;* by Joseph E. Pogt/e. 



The specimen under consideration (Catalogue No. 86362) 

 came into the possession of the United States National Museum 

 in 1908 with the acquisition of the Hambach Collection of 

 fossils and minerals. It was labelled " Mammoth Mine, Ari- 

 zona " ; no further information is available concerning its 

 occurrence. 



Fig. la. 



Fig. 16. 



Fig. la. Top view of cerussite twin. Projection on base, c = {001}. 

 Fig. 16. Bottom view of same. Projection on base, c = {001} 



Description. — Colorless, transparent. Dimensions 10x10 X 

 7 mm . Faces sharp and suitable for measurement^ Contact 

 twin, the two individuals nearly equally developed. Fig. la 

 shows the crystal as viewed from above, projected upon the 

 base o = |001| ; %. lb represents the under development of 

 the same crystal, projected also upon the base. In fig. 2 is 

 given a gnomonic projection of the upper half of the crystal 

 (as represented in fig. la), which shows clearly the relation of 

 the two individuals. 



* Published by permission of the Secretary of the Smithsonian Institution, 

 f The measurements were made on the two-circle goniometer in the min- 

 eralogical laboratory of Prof. V. Goldschmidt in Heidelberg. 



