pratt.] COKUNDUM GEMS. 43 
and smooth, making them well adapted for measurement on the 
reflecting goniometer. These crystals are shown on PL III. 
In the crystals examined two common habits were noticed; one is 
shown in figs. 1 and 2 of PI. Ill, and is a combination of the base c 
(0001) and the unit rhonibohedron r(1011); the other is represented 
by figs. 3-6 of PL III, where the prism a (11U0) is very prominently 
developed. The rhombohedral crystals vary from those in which the 
base and the rhonibohedron are disproport innately developed, the base 
having a diameter of 12 mm. and the rhombohedron of only 1.5 mm., 
to some (fig. 1 of PL III) in which Hie base and the rhombohedron 
are nearer one size. The majority of these crystals have, however, 
the base more largely developed, 11ms giving the crystals a flat, tabu- 
lar appearance. This rhombohedral development is vn-y similar to 
the sapphires from Yogo Gulch, Montana, described on page 52. ] 
On some of the prismatic crystals the prism reaches a length of 
nearly ir> nun. in the direct ion of thee axis, and has the rhombohedron 
/• but slightly developed (fig. :> of PL 111), while on others the prism 
is xi'iy short and the rhombohedron is sometimes wanting, as repre- 
sented in figs. 1 and 5 of PL III. 
Another habit of these crystals is shewn in tigs. 7 and 8 of PL III, 
where (he pyramid // (2243) is well developed. This face was identi- 
fied b\ means of t he contact goniometer, t lie measured angles approx- 
imating closely to those calculated. The usual form of these crystals 
is shown in fig. 7 of PL Ill, where the faces <■ (» 1 ),a(l L20), r(1011 ), 
and // (2243) are nearly equally developed. On some of the crystals 
the prism is very prominent, being 8 mm. in length in the direction of 
the c axis, while the pyramid is only L.5 mm.; on others the pyramid 
is only very slightly developed. A few crystals were examined which 
showed only t he presence of 1 he base, the rhombohed ron, and 1 he pyra- 
mid, as represented in tig. 8 of PL III. The crystals, measuring up 
to 7 mm. in diameter, were doubly terminated and nearly perfect in 
their development. 
The crystals represented by fig. 7 of PL III are similar to those 
described by Bauer 2 from the Burma district, and are almosl identical 
in form with the sapphire crystals figured by me, \'v Emerald Bar, 
Canyon Ferry, Meagher Con nty, Mont. (p. 50). 
Although both the basal and rhombohedron planes are very often 
striated, it is only on the basal planes that the striatums are sharp and 
distinct and can be measured. The striatums are parallel to the three 
intersections of the base c and the rhombohedron r as shown in tig. 5 
of PL III. 
A very common development that was noticed on nearly all the flat 
rhombohedral crystals and on many of the prismatic crystals is a 
1 Also Am. Jour. Sri.. 4th series, Vol. IV, 1897, p. 124 
2 Neu(« Jahrbuch fur Min., Geol., und Pal., Vol. XI, 1896, p. 209. 
