900 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



part possesses a brownish-yellow or even a reddish-yellow color. This 

 is often most pronounced about black oxide inclusions and is thought 

 to be due to a pigment stain of ferruginous character. There at least 

 appears to be no regularity aliout the distribution of these discolora- 

 tions. The optical characters are otherwise the usual ones for 

 aegirite. 



In thin-sections from the quarries from the western half of the area 

 a dark red mineral has been noted associated with the hornblende and 

 aegirite. Its presence appears to have been first noted by Murgoci ^'^ 

 who thought it to be a new mineral and tentatively suggested the name 

 Quincyite for it. It appears to be of rather rare and somewhat 

 irregular occurrence. Its crystals are for the most part small and 

 its depth of color render them unfavorable for satisfactory study. 

 So far as determined its properties are as follows : — cleavage-good, 

 apparently prismatic, resembling that of hornblende; pleochrism- 

 deep red or brownish to almost black for the ray making an angle of 

 30° to 40° with the cleavage; ray perpendicular to this, a bright 

 mahogany-red. Double-refraction weak. The extinction angle is 

 too large for any of the alkali amphiboles and the only mineral that 

 seems to agree with these characteristics is aenigmatite. It is com- 

 monly, though not always, in parallel position with aegirite or horn- 

 blende and its contacts are usually rounded. It is also seen in the 

 form of small, usually rounded grains sometimes enclosed in aegirite 

 and also closely associated with masses of granular zircon. It has 

 been noted also in close association with astrophyllite — apparently 

 secondary after it — and on one instance it was noted largely replaced 

 by this mineral. V. Hackman has descriljed a secondary mineral 

 having apparently properties very similar to, if not identical with 

 astrophyllite, surrounding aenigmatite in the nephelite syenite from 

 Umptek.i^ 



Fluorite, as has been noted, occurs as included grains in the earlier 

 aegirite and is often cjuite abundant there; it is also found, though less 

 commonly, in the hornblende. Single grains or more often clusters 

 or compact granular aggregates are sometimes seen associated with 

 the quartz, and in such cases zircon and hematite are often present 

 also. It has been noted that fluorite is apt to be more abundant in 

 the granite where it is cut by small quartz veins. Zircon tiJmost 

 always is found in close association with quartz and rarely forms well 



17 Private correspondence. 



18 MilvTOskopische Physiographic, Rosenbusch, p. 384. 



