wherry: neodymium, cause of red-violet color 145 



red-violet 5 calcite from Joplin, Missouri, gives this neodymium 

 absorption spectrum. This was confirmed by the writer in 

 the paper referred to, and in addition it was noted that the 

 red-violet calcite from Rossie, New York, shows, faintly, the 

 same spectrum. Specimens from Sterlingbush, New York, re- 

 cently received by the National Museum in exchange from the 

 New York State Museum, have the same color as the latter oc- 

 currence, and show the same absorption spectrum. 



That manganese is not the cause of the color of these calcites 

 is shown by the following considerations: The calcites con- 

 tain ferrous iron, and must accordingly have been formed under 

 reducing rather than oxidizing conditions, so that any manga- 

 nese present must be in the manganous state. Now manganous 

 carbonate, the mineral rhodochrosite, is pure red in color, and 

 that this color is not essentially changed by association of the 

 manganese with calcium is evident from the pale red color of the 

 so-called manganocalcite, such as occurs for instance at Franklin 

 Furnace, New Jersey. Furthermore, many calcites known to 

 contain moderate amounts of manganese show no color whatever. 

 The minute trace of manganese present in these red-violet cal- 

 cites could therefore not bj^ any possibility produce their color. 



There is thus both positive evidence (the absorption spec- 

 trum) and negative evidence (the inability of manganese to pro- 

 duce the color) in favor of the view that red-violet calcite in 

 general owes its color to neodymium. 



The mineral apatite is sometimes violet in color, but, as re- 

 corded in the writer's paper above cited, usually shows no ab- 

 sorption spectrum. Oddly enough the well known brown apatite 

 from Ontario, Canada, yields the absorption bands of neodym- 

 ium, although any red-violet color that this metal produces is 

 masked; most of the crystals show an underlying green color, 

 due presumably to ferrous iron, the brown being only a sort of 

 local mottling which could readily be produced by irregular 

 distribution of a pale red-violet coloring matter. 



6 An effort was made to name the colors of these calcites according to Ridg- 

 way's "Color standards and nomenclature," but accurate comparisons of colors 

 seen only in thick layers of a transparent mineral and those painted on sheets of 

 paper are impracticable. The approximate position of the calcite colors is, how- 

 ever, 67, violet-red, composed of red 52 per cent, violet, 48 per cent. 



