Science of the International Exhibition. 259 
value. In this collection were specimens of a magnesian mica, or phlog- 
opite, from South Burgess, which quite recently has been found to ex- 
hibit the rare property of asterism in a remarkable degree. This has led 
to a new examination of the subject, and now this hitherto obscure point 
In optical mineralogy can be readily and satisfactorily explained. The 
asterism of this mica was, I believe, first observed by H. Vogel, of Berlin, 
during a recent visit to the exhibition. On his return he investigated 
the subject in company with Prof. G. Rose, who had observed a similar 
appearance, although much less distinct, in some varieties of meteoric 
Iron, Prof. Rose has just communicated the results of the investigation 
to the Royal Academy of Berlin,‘ and the subject is of such general in- 
terest that the main points of his paper may not inappropriately be given 
in this connection. 
are clongated, flattened prisms, having the broad lateral planes par- 
allel With the lamine of the mica. Their resemblance to crystals of 
kyanite is quite marked, and it is very probable that they belong to that 
tes. Tabular crystals, also, may be seen, which are apparently quite 
r prisms. e i e i ave a 
or ° 
asterism is easily explained. It is a mere “trellis-appearance” (@itterer- 
scheinung); and the rays of the star stand at right angles to the axes of 
those prismatic crystals which make with each other angles of 120°, and 
hence proceed from the center of the star to the middle of the sides of 
parallel. 
it has been observed, is the same as in the present instance. 
nthe sam paper, Prof. Rose gave the results of his examination of 
the asterism in meteoric iron, and referred to the previous investigations 
on this interesting subject. 
| , Nov, 25, 1862. 
~ 
de G. Rose, Ueber den Asterismus der Krystalle, insbesondere des Glimmers und 
Meteoreisens, Oct. 30, 1862. See also Phil, Mag., Jan. 1863. 
