Chemistry and Physics. | 435 
to the base of the original hexagonal crystal, may be facilitated 
by a grouping of the molecules of the tourmaline, in the manner 
represented g. 
have also a plate of amethystine quartz, in which a beam of 
eal divergence of several degrees; and, on one other plate of 
amethyst we have had an opportunity of examining, we have al 
seen under the polarizing mlocoenageais biaxial curves at one or 
more points. : 
These facts most distinctly suggest the theory that the optical 
phenomena of quartz are produced by a molecular structure simi- 
o tha 
artificial plates of mica, and that the two orders of crystals are 
aggregates of compound molecules, whose parts are twinned 
together in the one case in ri ht-handed, and in the other in left- 
handed spirals, and, lastly, that the simple molecule, if developed 
ld produce a biaxial structure.* eory is 
* Since the above in type, we have received Am. Jour. Sci., IV., February, 
Peat: containing a description of the rhombic silica which Prat Maskelyne, of the 
use has discovered in the meteorite : 
Thoma! Silica, which Prof. Maskelyne calls Asmanite, has the form of a right 
sem prism, with an angle of 120° 20’, and gps prey are optically biaxial ; 
© the speci ity of quartz is 2°6 o it 
2°245. Tt ig WD tinea ge! ole that such a molecular macling as _ +t 
described would ine an increase of density, since thereby three re gan 
be to form one; or it is possible that the remarks made SS 
pliiney *PPIY also to quartz; but still the marked difference remains 
