478 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.58. 



A portion of the analyzed powder has been preserved in the type 

 materials series as is the practice here and is available should it be 

 desirable to recheck these values. The values given above for mean 

 refractive index and birefringence approach those of zoisite, as is to 

 be expected in material of such low iron content. The fluorine, which 

 occurs in small amount, is of interest, since fluorine has not hereto- 

 fore been noted as a constituent of epidote,' although it is to be ex- 

 pected that fluorine would replace the basic hydroxyl of epidote as- 

 readily as that of other similarly constituted minerals. Fluorine 

 seems to have been abundantly present in the emanations forming the 

 Long Hill veins, and a constant content of fluorine runs through all 

 the minerals of the area, as noted under scapolite and margarite 

 below. 



TOPAZ. 



Topaz is present in the quartz veins in quite unusual amount. The 

 best locality is that described as the Limekiln Vein. This vein, which 

 has been opened for a distance of some 75 feet, is from 1 to 5 feet 

 wide. The vein originally consisted almost entirely of quartz and 

 topaz, the quartz being considerably more abundant than the topaz. 

 An extensive alteration, probably under deep-seated conditions not 

 dissociated from a stage in the regional metamorphism of the area, 

 has resulted in the partial conversion of the topaz to secondary 

 minerals. The alumina of the topaz has gone to form muscovite of 

 the variety known as margarodite with less margarite. The fluorine 

 has combined with lime probably derived from the marble of the 

 walls to form fluorite. 



The topaz occurs in coarse crystalline masses of gray to pale yellow 

 or white color, with well-defined cleavage, some of the cleavage 

 surfaces being a foot in diameter. Most of the topaz contains veins 

 and disseminated scales of margarodite, and large masses of mar- 

 garodite contain cores of corroded and embayed topaz. Where the 

 topaz abuts against small open cavities in the center of the vein it 

 is bounded by rough crystal planes. Many of these cavities have 

 been filled with coarse foliated margarodite not derived from the 

 adjacent topaz crystals, as the surfaces of these crystals are not 

 corroded. 



In the main pit topaz occurs in greenish nodular masses with 

 poorly defined cleavage, now in part altered to margarodite, in the 

 narrow quartz veins which contain black sphalerite. Topaz of the 

 same type occurs in several other smaller veins. The foliated mica 

 margarodite occurs everywhere in the quartz veins, and this type 

 of mica seems in all cases to have been derived from the alteration 

 of topaz even where no topaz now remains. 



» An epidote from Italian Mountain, Gunnison County, Colo., analyzed by Eakins, con- 

 tained 0.35 per cent of fluorine, U. S. Geol. Survey, Bull. 591, p. 316, 1915. 



