4 PBOOKEDINC.S nF Till: AMERICAS ACADEMY. 



has t>ccn made on the impurities which are present in the natural min- 

 eral The first of these investigations 9 was made on the gases con- 

 tained in fluorite, and the results of this research are wholly negative 

 as far as the question of the source of luminescence is concerned. 

 N ithing other than the ordinary gases was found in any case, and do 

 relation between the occluded gases and the emission of light under 

 excitation was discovered. 



At the present time, careful chemical analyses of a Beries offluorites 

 from many parts of the world are being carried out, in the hone of find- 

 ing a due to the source of the light emission. The results of tl 



analyses, as lar as they have gone, are must interesting. Many fluorites 



are found to contain quite evident amounts of rare earth-; 1 and from 



<>ne specimen, at least, enough ueodymium and pras lymium h 



been separated t<» give a quite measurable absorption spectrum. The 

 author intends to report the results of these investigations to the 

 American Academy as soon as possible, 



II. The spectra of a large number of fluorites, excited by kathode 

 rays, have been examined and photographed. Of this large number, 

 in will be described in this paper. The crystals examined were : 



1. Pluorite from Amelia Court-House, Virginia. This region is a 

 famous i »ne because of the occurrence of this Huorite, which has re- 

 markable properties, and also for many other minerals containing rare 

 earths. Very large rnicrolite crystals were found near the Huorite de- 

 p"dts. The crystals of iluorite from this region are what are called 

 "chlorophanes," jxir excellence. They are very sensitive to heat, emit- 

 ting light strongly at the temperature of boiling water, and so strongly 

 at 300° as to be bright objects even in a well-lighted room. The iluor- 

 ites occur in colors varying from dark brown and dark purple to light 

 green. All show the same thermo-luminescence .spectrum, and the 

 same kathododuininescence spectrum. The spectrum of thermo-lumi- 

 nescence of this variety has been given at length in a previous paper. 8 

 The details of the kathodo-luminesccnce spectrum arc given in Table I, 

 and the appearance of this spectrum is seen in Figure 1, Plate o. 



2. Fluorite from Trumbull, Conn. This is also a brilliant "chloro- 

 phanc," which shows the same thermo luminescence spectrum as the 

 Virginia crystals, and a kathodo-luininescence spectrum which is very 

 closely related to that of the other mineral. Details of the latter 

 spectrum are given in Table II, and the appearance of the spectrum is 



in Figure 2 of the plate. 



3 Studies on Fluorite, III. These Proceedings, 41, 601 (Mar. 1906). 



4 See also Humphreys, AstrophysicalJournal, 20, 266 (1004). 



6 Studies on Fluorite, II. These Proceedings, 41, 698 (Mar. 1908). 



