ART. 9. MINERALOGIC NOTES ON PUCHERITE, ETC.-—SHANNON. r 
symmetry. Examination in polarized light of the measured crystals 
shows these to be twins, as shown in Figure 7, made up of biaxial 
orthorhombic sectors. The sectors. have interlocking boundaries. 
Each sector has a well-defined cleavage parallel to its free edge, and 
the extinction is parallel to this edge. Each sector gives in conver- 
gent light a perfectly centered biaxial interference figure. ‘The several 
apparently prismatic planes of the pseudo-hexagonal tablet thus are 
evidently pinacoids of the several orthorhombic units which go to 
make up the twinned group. This may indicate that the ortho- 
rhombic form is an inversion product which is pseudomorphous after 
an original hexagonal form, but it is more probable that it is merely 
characteristic of trichalcite to form repeated twins, with the twin- 
ning plane the unit prism i 
(110), which are pseudo- = ahi) RY 
hexagonal. This is char- Ls Son 
acteristic of a great (PS De: } 
many orthorhombic min- 
erals whose prismatic 
angle approaches the 
hexagonal angle, as, for 
example, aragonite, with- 
erite, cerrussite, chalco- 
cite, etc. Figure 8 is 
drawn to show, in ortho- 
graphic and clinographic 
projections, a _ crystal 
which, while having the 
same tabular habit, is 
untwinned. 
Trichalcite has previ- 
ously been known only Fas. 9-10.—ORTHOGRAPHIC AND CLINOGRAPHIC DRAWINGS OF 
from the original locality WAVELLITE CRYSTALS FROM ARKANSAS. 
in the Urals, the Idaho 
occurrence thus giving a second locality for this rare arsenate. The 
associated arsenates in the Idaho specimen have not been identified. 
These include a yellow-green material resembling scorodite and a 
green mineral resembling clinoclasite. 
~ 
—— 
10 
WAVELLITE CRYSTALS FROM ARKANSAS. 
A specimen in the Museum collection (Cat. 45211) which shows mi- 
nute white to brownish-white acicular crystals implanted singly and 
in groups over surfaces of gray-green variscite was labeled ‘‘natrolite 
on variscite.” The specimen was received from Mr. Charles F. 
Brown and bore this label when received. The unusual association 
of a zeolite with a phosphate had not previously been noted, and this 
60466—23—Proc.N.M.vol.62— 30 
