KO.2220. COLOICED VARIETIES OF QUARTZ— WATSON d BIJAIW. 657 



minutes in the flame of a No. 4 Meker burner, which yields a tempera- 

 ture of 1,120-1,140° C. Exact measurement of tlie tempera turo to 

 which the minerals were subjected was not made, but it was proba])ly 

 around 1,100° C. 



The results of these tests were that the original color of four speci- 

 mens of amcthj^st, eight of rose quartz, and one each of green and 

 purple fluoritc and green feldspar (aniazon stone) was completely 

 destroyed. The minerals were completely decolorized on heating, 

 with the single exception of the deep green feldspar from Amelia 

 County, Virginia, which assumed a faint pinkish color after cooling, 

 due probably to the presence of ferric oxide. The luster on the cleav- 

 age surfaces of the feldspar was not affected by the lieating. 



The color of the deep blue quartz from Nelson County, Virginia, 

 was unaffected after heating for two periods of 10 minutes each, 

 except that a pronounced red color developed along original fracture 

 lines in the mineral on cooling. No change in the original color 

 for other portions of the mineral was observed. Robertson * noted 

 that after fusing a fragment of the blue quartz from the samelocahty 

 before the hot-blast blowpipe flame, the mineral retained its color. 



From the results obtained by others it is probable that the color 

 of the minerals tested by the writers would have been destroyed at a 

 lower temperature and in a shorter period of heating. After an 

 exposure for seven months to daylight there is slight indication of 

 the return of the original color in the decolorized specimens of 

 amethj^st and fiuorite, but not in the rose quartz, blue quartz, or 

 green feldspar. 



DISCUSSION OF RESULTS. 



Amethyst. — The amethystine color of the amethyst variety of 

 quartz has been attributed to the presence of a variety of substances 

 by different investigators, but it has been generally assumed to bo 

 due to the presence of manganese oxide dissolved and diffused through 

 the quartz. Manganic oxide, titanic oxide, sodium ferrate, iron 

 eulphocyanate, and organic matter are substances that have been 

 reported by different writers as the cause of amethystine color in 

 quartz. 



Nabl 2 suggested in 1899-1900 that the coloring matter of amethyst 

 is due to the presence of iron sulphocyanato, because the absorption 

 spectrum of amethyst seemed to him to bo about the same as that 

 of this compound in ether solution; and he bcheved that he estab- 

 lished tliis further by analyses showing the presence of sidphur and 

 nitrogen. The more recent work of Berthelot and Simon, briefly 

 summarized below, does not bear out this suggestion. 



> The \ irglnias, 1SS5, vol. 6, p. 2. 



« Sitzber. A.l:ad. Wiss., VVJen, 1899, vol. 2; Mln. mid Petrog. Mitth., 1900, vol. 19, p. 27.'«. 



