1355 
very beautiful Röntgen-pattern obtained by means of a section perpen- 
dicular to the principal axis (d—0,24 mm.) appeared to possess 
not only a quaternary axis, but also four vertical planes of symme- 
try passing through it. Moreover, also the images of plates parallel 
to (100) and (410), which had a thickness of resp. 0,19 and 0,18 
mm., showed the presence of two planes of symmetry perpendi- 
cular to each other, and a binary axis. The original photos are 
reproduced in figs. 2 and 3 on Plate I, while their stereograpbical 
projections are published in figs. 7, 8 and 9 on Plate IV. The men- 
tioned phenomenon may be observed therein immediately as well as 
the great number of spots; not the slightest indication can be found 
pointing to a lower degree of symmetry of these images. 
It is natural to give an analogous explanation of this abnormal 
behaviour in the same way, as formerly was given in the case of 
quartz, namely by supposing a twin-structure to be the canse of it. 
Indeed scheelite often shows a twin-formation, which could be the 
cause of this strange behaviour: not seldom scheelite-twins are found 
with parallel axial-systems, which may be considered to be penetra- 
tion-twins with an apparent symmetry after four planes, passing 
through the vertical axis; the RöÖNrGeNograms of such a penetration- 
twin would indeed show the symmetry observed by us. But our 
crystals showed neither a striation of the pyramidal faces, nor the 
occurrence of angles, nor any further indication for the correctness 
of the supposition, that really such a penetration-twin is present 
here. Of course an optical investigation cannot decide the question 
here in any way. 
We tried to find out also the normal case, by studying in the 
same way a number of scheelite-crystals of the best quality, and 
from all kinds of places: from Praversella in Piemont, from Kammegg 
in Guttannen (Berner Oberland), from Schwarzenberg, ete. In fig. 4 
of Plate [ we have again reproduced one of these photos, obtained 
with a plate parallel to (OOI), and 0,26 mm. thick, cut from a 
crystal of Guttannen. But also here there could be no doubt whatever 
about the fact, that the RÖNtGeN-patterns of all these scheelite-crystals 
showed quite the same phenomenon. The image e.g. of the crystals 
from Traversella, although not completely centrically orientated, 
showed clearly the presence of planes of symmetry. 
We must therefore conclude from this, that even externally per- 
fectly single individuals of scheelite, in reality must be polysynthetic 
intergrowths of right- and left-handed crystals. We do not see that 
another explanation of the observed phenomenon is possible in this 
case, if not after all one were inclined to doubt the essential correctness 
