W. P. Headden—Some Phosphorescent Calcites. 301 



Art. XXVI. — Some Phosphorescent Calcites from Fort Col- 

 lins, Colo., and Joplin, Mo. / by Vm. P. Headdetst. 



The calcites discussed in this article possess the property of 

 becoming phosphorescent on being insolated and retain this 

 property, in some cases, for a period of thirteen hours. Ordi- 

 nary calcite under like conditions phosphoresces for one-third 

 of a second and aragonite for twenty seconds. Many other 

 minerals become phosphorescent on being insolated, but the 

 duration of this phosphorescence is very brief. 



The specimens described in this article are from two locali- 

 ties, Fort Collins, Colo.- and Jo pi in, Mo. The Colorado speci- 

 mens occur as a vein of calcite cutting through the Fort 

 Benton shales. No distinct crystals have as yet been found 

 at this locality. The specimens from this locality are inferior 

 to the Missouri mineral in all respects, particularly in regard 

 to the brilliancy of the phosphorescence. The best specimen 

 from this locality was quite strongly phosphorescent after inso- 

 lation, it was observed for two and one-half hours, when the 

 observation was abandoned though the specimen was still phos- 

 phorescent. 



The Missouri specimens occur in two forms, both in well 

 defined crystals. One is the well-known dog-tooth spar, only 

 slightly modified by a vhombohedron ; the other is a combina- 

 tion of two scalenohedrons. The crystals of clog-tooth spar 

 are as a rule quite large, and have, exteriorly, a yellow color ; 

 the crystals showing a combination of two scalenohedrons are 

 smaller and their interior portion is yellow, while the outer 

 portion is colorless or in some instances slightly violet. The 

 change from the yellow to the colorless calcite in these crys- 

 tals is sometimes shown very distinctly by a crop of chalcopy- 

 rite crystals which have formed on the surfaces of the more 

 obtuse scalenohedron. 



The Missouri specimens show a stronger phosphorescence 

 and are in other respects better fitted for the purposes of this 

 investigation than the Colorado ones. The following data, 

 therefore, have been obtained from the Missouri mineral. 



The occurrence of wine-colored crystals of calcite at the 

 lead and zinc mines near Joplin, Mo., is well known, but 

 I do not know the mine or mines from which my specimens 

 were obtained. In the case of the dog-tooth spar, the wine- 

 yellow color is due to the deposition of a yellow calcite in the 

 last stages of their growth. The interior portions of these 

 crystals are seldom if ever yellow, but are colorless or violet if 

 transparent and white if opaque. The other type of crystals 

 have yellow centers and a colorless or violet-tinged outer 

 portion. 



