1215 
henitoite ; it appears to be composed of lamellae, which with respect 
to each other are turned through an angle of 120°, and seem to 
possess rhombic-hemimorphic or monoclinic symmetry. | 
The plates parallel to {1010} and {1210} also betrayed this lamellar 
structure in a more or less convincing way: the plate parallel to {1210} 
showed this lamellar character very clearly, and was composed of 
two sets of nearly perpendicular crossing lamellae, which made 
about 53° with the c-axis, while an irregular partition in fields of 
different colour and dichroism could be observed in some cases 
besides. 
The crystals are very strongly dichroitie: for vibrations parallel 
to the c-axis the crystals have a deep blue colour, for such perpen- 
dicular to the c-axis, they are almost colourless, with a very faint 
lilac hue. 
The cleavage is very imperfect, and parallel to {1014}; from the 
goniometrical measurements it follows, that the psendo-trigonal 
complex has an axial ratio of: a:¢ =1: 0.73819. 
In figures 12, 15, 14, are reproduced the stereographical projections 
of the very fine RÖNrGeNograms which were obtained in our expe- 
riments. Figures 9,10, and 11 on plate III are reproductions of the 
original photographs. 
The plate perpendicular to the c-axis (fig. 14) gave a R6NTGEN- 
pattern, which possessed no more than one single plane of symmetry, 
parallel to 11010} notwithstanding its undeniable trigonal design. 
In agreement with this, the image in fig. 13, obtained with a 
plate perpendicular to {1210%, shows a vertical symmetry-plane. Lt 
may appear doubtful whether this image also possesses a horizontal 
plane of symmetry: a very slight but noticeable difference in the 
intensity of the spots at the ends of the vertical axis seems to be 
present. 
The question is however, whether this would indicate a real, and 
in that case very feeble polarity of the c-axis, or if it should be 
considered as a photographic effect, caused perhaps by a slight 
deviation of the plate from its normal position. In fig. 12, obtained 
by transmission of the pencil of R6ONTGENrays in a direction perpen- 
dicular to {1010}, the polarity of the c-axis is however very much 
more easily recognisable, — not only in the differences in intensity, 
but also in the different arrangement of the spots. 
However, whether one considers the c-axis a polar one or not, 
the combination of the symmetry-properties observed is here geome- 
trically quite impossible also; for if the c-axis is of a polar nature, 
