14 



PROCEEDINGS OF THE NATIONAL MUSEUM. 

 Angles of zircon crystal from Rosa, Bingham County (fig. 9). 



VOL. 60 



This looks very much like zircon, but the angles are nearer those 



of rutile, although the measurements are not sufficiently exact that 



it may be referred to that mineral. One or two crj^stals having the 



same form as the last and an orange-red color were seen in a sand 



from Minidoka but were not measured. One of the most unusual 



iyg^s of tetragonal crystals seen occurs in the Minidoka sand and is 



long acicular, the length being 10 to 20 times the diameter. These 



crystals show only the unit prism m(llO) and the pyramid ^(111), 



as shown in jBgure 7. The crystals of this long prismatic type are 



all pale pink in color. One which was measured gave the following 



angles : 



Angles of zircon crystal from Minidoka (fig. 7). 



The only other type of tetragonal crystals seen was bipyramidal 

 showing no prism faces, only the form p (HI) being present. This 

 habit is illustrated by figure 8. Crystals of this habit having an 

 orange-red color occurred rarely in a sand from Snake River in 

 Ada County and a few having a brownish-white color were seen in 

 the samarskite-columbite concentrate from Idaho City. Accurate 

 measurements could not be obtained from these crystals owing to 

 their small size and imperfect faces. 



While all of the above-described tetragonal minerals are referred 

 to zircon, comparison of the angles will show, as previously men- 

 tioned, that several of the types, especially the latter less common 

 ones which have orange or brown colors may equally well be thorite, 

 xenotime, or a light-colored rutile. The measurements were in no 

 case sufficiently accurate or dependable to serve as evidence for 

 differentiating between these tetragonal minerals which differ only a 

 few minutes from each other in angles. It is comparatively certain, 

 however, that zircon is the only abundant tetragonal mineral pres- 



