102 CORUNDUM, ITS OCCURRENCE AND DTSTRTBUTTON. 
reflecting goniometer, the faces were readily identified by means of 
the contact goniometer. On some of the crystals the faces were 
bright and smooth, making them aa-cII adapted for measurement on 
the reflecting goniometer. These crystals are shown on PI. V. 
In the crystals examined two common habits were noticed; one is 
shown in figs. 1 and 2 of PL V, and is a combination of the base c 
(0001) and the unit rhombohedron r (1011) ; the other is represented 
by figs. 3-6 of PI. V, where the prism a (1120) is very prominently 
developed. The rhombohedral crystals vary from those in which the 
base and the rhombohedron are disproportionately developed, the 
base having a diameter of 12 mm. and the rhombohedron of only 1.5 
mm., to some (fig. 1 of PI. V) in wdiich the base and the rhombohedron 
are nearer one size. The majority of these crystals have, how^ever, 
the base more largely developed, thus giving the crystals a flat, tabu- 
lar appearance. This rhombohedral development is very similar to 
the sapphires from Yogo Gulch, Montana, described on pages 
113-114.« 
On some of the prismatic crystals the prism reaches a length of 
nearly 15 mm. in the direction of the c axis and has the rhombohedron 
r but slightly developed (fig. 3 of PL V), wdiile on others the prism 
is very short and the rhombohedron is sometimes wanting, as repre- 
sented in figs. 4 and 5 of PL V. 
Another habit of these crystals is shown in figs. 7 and 8 of PL V, 
where the pyramid n (2243) is well developed. This face was identi- 
fied by means of the contact goniometer, the measured angles approxi- 
mating closely to those calculated. The usual form of these crystals 
is shown in fig. 7 of PL V, where the faces r (0001), a (1120), r (lOTl), 
and n (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, Avhile the pyramid is only 1.5 mm. ; on others the pyramid 
is only very slightly developed. A few crystals were examined which 
showed only the presence of the base, the rhombohedron, and the 
pyramid, as represented in fig. 8 of PL V. 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 V are similar to those 
described by Bauer ^ from the Burma district, and are almost identical 
in form with the sapphire crystals figured by me, from Emerald Bar, 
Canyon Ferry, Meagher County, Mont. (p. 109). ■ 
Althougli both the basal and rhombohedral planes are very often 
striated, it is only on the basal planes that the striations are sharp and 
distinct and can be measured. The striations are parallel to the three 
intersections of the base c and the rhombohedron r, as shown in fig. 5 
of PL V. 
" See also Am. .Toar. Sci., 4th ser., vol. 4, 1897, p. 424. 
"Neues .Tahrbuch fiir Mineral., (ieoi., und Pal., vol. 11, 1S!)<5, p. 209. 
