Hidden and Washington— Contributions to Mineralogy. 507 
The basal pinacoid was rare, —$A, +H and & predominated. 
One crystal was terminated almost wholly by $2. 
QUARTZ.—Vom Rath has already called attention to the oc- 
currence of the plane &, = (4180) 7-4 on quartz crystals from 
Alexander County, North Carolina.* Its best development 
seems to have been found on crystals from the gem mine, in 
Sharpe’s township. Thus far this plane has been described as 
‘Ca hemihedral twelve-sided prism,” and its fine vertical stria- 
tion and often observed right-angled intersection with the trap- 
ezohedron 4-4 (4131) at once characterized it and made it easily 
recognized. Quite recently we have obtained several crystals, 
from this same locality, which apparently presented this plane 
holohedral, in pairs on each consecutive prismatic edge, instead 
of on alternate edges as before noted. 
Vom Rath’s measurements gave as the angle of k,,g (/) 
13° 52’ (calculated 18° 54’), while we found &,,k, adjoining 
= 31° (calculated 32° 12’). One of the new crystals (8x43) 
exhibited this rare plane 18™" wide and 19™™ long. 
We add also to this paper notices of a new plane on topaz 
and a twin of corundum. 
Topaz.—This was a clear white acu of about 1x 2°, 
which was sent to us from the noted locality near Zacate- 
cas, Mexico, where they are found in the detritus of trachyte 
very similar to the occurrences in Utah described by Alling ft 
and in Colorado by Cross. This crystal had the usual habit of 
topazes from Durango. Replacing the solid angle formed by 
110, 110, and 201, there was observed a new plane which has 
the symbol (701, if 2). A comparison of its observed and cal- 
culated angles is here given: 
Calculated. Observed. 
001 4 701 80° 58” 81° 67 
110, 701 8° 292” 8° 317 
CorunDUM.—A twin of corundum was found among a lot of 
gem material received from Ceylon. Its high polish and 
twinned form are features rarely observed in the species. It 
was of a clear grayish blue color. Both basal pinacoids were 
present and were highly polished. The angle observed be- 
tween the two was 114° 20’, giving as a twinning plane the 
unit rhombohedron. 
* Sitzungsberichte der Niederrhein. Gesellsch. f. Nat.-u. Heilkunde, 6 July, 
1885. Zeitschrift fir Krystallographie, etc. xii, 456. 
+ This Journal, III, xxx, 146, 1887. 
