1903.] WRIGHT—CRYSTALLOGRAPHIC PROPERTIES. 245 
all conditions of concentration and temperature only very slightly. 
In one experiment with cold HCl (1 part concentrated HCl 30.5 %, 
Sp. g. == 1.515 with 1 part water, time of exposition 7’), however, very 
small etch figures with sharp hexagonal outline were produced, not 
unlike those resulting from nitric acid. Their edges ran also paral- 
lel to the outer crystal edges. The absence of one set of parallel 
lines in the vicinity of that outer edge to which it was parallel was 
also observed on one crystal, etched with HCl. It is noteworthy 
that in this chemical process no noticeable gas bubbles are seen to 
escape. 
Both the crystallographic measurements and the etch figures seem 
thus to prove the hexagonal nature of artificial domeykite crystals. 
On the following minerals, however: argentodomeykite, stibio- 
domeykite and mohawkite, the basal plane was so poorly developed 
that good, trustworthy etch figures could not be obtained. Their 
crystallographic system was deduced solely from the goniometric 
measurements. 
In a recent article’ on artificial domeykite crystals, Mr. Stevano- 
vics considers the crystals examined by him to be orthorhombic, 
notwithstanding the hexagonal symmetry of his measurements, and 
bases his conclusions on the appearance of a cleavage after the 
macropinacoid, 100. A careful investigation by the present writer 
confirmed the cleavage noted above after three faces 60° apart. The 
cleavage seemed equally good after all three faces. In certain pieces 
cleavage fragments of perfect hexagonal outline (equilateral tri- 
angles) were produced. On the goniometer the angle between two 
such cleavage faces was found to be approximately 60°. The basal 
plane was uneven and did not permit an exact adjustment of the 
crystal. 
The elements and forms described by Mr. Stevanovics were the 
following : 
Orthorhombic: @ :.6: ¢ =0.5771: 1: 1.026 
Forms: ¢ m 6 p a v g 2 Cea asige ng bee q? 
oor Ifo O10 IIL O2% I12 OF I13 023 043 O41 0.5.12 
with ¢, ~, g rare and uncertain. 
As hexagonal crystals these elements and forms become: 
1 Zeitschr. f. Krystallographie, Vol. xxxvii, pp. 245-246, 1903. 
