NO. Ii220. COLORED VARIETIES OF QUARTZ— WATSON d BEARD. 561 



of color destroyed by heat in the case of rose quartz, which proves 

 that the color is due to organic and not to inorganic substances.' 



Dana^ quotes Fuchs as stating that the color is due to titanium, 

 since he found 1 to 1.5 per cent in specimens from Rabenstein, near 

 Bodenmais, and the former (Dana) then remarks that it may come 

 in part from manganese. 



From the chemical nature of the metallic substances determined on 

 analysis to be present in rose quartz, the character of inclusions 

 found on microscopic study of thin sections, the complete absence of 

 the shghtest indication of the original color being restored in the 

 decolorized specimens on heating after exposure of seven months to 

 dayhght, and the lack of restoration of color destroyed by heat on 

 exposm-e to rachum rays by Doelter, the writers conclude that the 

 color of rose quartz can not be attributed to an inorganic substance. 



Blue quartz.— By way of contrast it may be of interest here to 

 briefly summarize the results of the investigations into the cause of 

 blue color in some quartz. The occurrence in quantity of beautiful 

 deep sky-blue opalescent quartz in quartzose igneous rocks and at 

 times in metamorphosed sediments derived from them, is known in 

 many locahties both in this country and abroad, and has been the 

 subject of investigation in a number. This variety of quartz is b}^ no 

 means uncommon in the Southern Appalachians, and is particularly 

 characteristic of some rock types of the Blue Ridge Mountains and 

 its outhers in Virginia. 



The senior writer has examined microscopically many thin sections 

 of blue quartz from different localities in the southeast xVtlantic 

 States, and in every case the substance of the quartz was found to 

 be crowded with hairhke inclusions of rutile, which were frequently 

 arranged with more or less crystallographic regularity. On the other 

 hand, quartz of hght color or colorless to dark smoky often shows 

 inclusions of rutile needles, with no indication whatever of blue color. 



The blue color of the quartz was apparent in thin sections as well 

 as in hand specimens. There is no evidence, however, that the 

 included crystals of rutile observed in the quartz are blue in them- 

 selves, although Dana records among the varieties of color for rutile 

 bluish and violet shades. Of the well-known laboratory tests for 

 titaniimi, two impart a violet color (1) to the salt of phosphorus 

 bead in the reducing flame when cold and (2) to a hydrochloric acid 

 solution when boiled with metallic tin, but neither compomid of 

 titanium (TijOg and TiCl,), supposed to produce the color, is laiown 

 to occur in nature. 



I See p. 559 of this paper for amount of manganous oxide (MnO) found by George Steiger in rose quartz 

 from Creede, Colorado, and description of laboratory experiment. 

 - A System of Mineralogy, 1892, p. 187. 



77408— Proc. N. M. vol. 53—17 36 



