1 887] Mineralogy and Petrography. 663 
discussion Flink mentions the fact that he has become possessed 
of a large collection of good crystals from Pajsberg and Langban. 
These he examines, and finds on them nineteen forms new to the 
species. The axial ratio as calculated from his measurement is: 
a:b:c=1.0727:1:0.52!104. The inclinations of the axes to 
each other are a = 76° 41’ 52/7, 8==71° 15’ 15”",7 =81° 30’ 16”. 
The plane of the optical axes is inclined to oP and œP at 63° 
and 384° respectively. It corresponds to $,P1%,3,P1®. The acute 
bisectrix is perpendicular to the plane PTT and is probably 
negative. 2Va= 76° 12’ for sodium light and p < v absorption 
b>a>c—. The intergrowth of minerals of analogous com- 
position has within the past few years been proven to be very 
much more common than was formerly supposed. The micro- . 
scope has revealed the fact that very many rock-forming minerals, 
as, for instance, the pyroxenes and the feldspars, very frequently 
occur intergrown with lamellz of analogous but slightly different 
composition. The method of etched figures has shown the same 
statements to hold good in regard to minerals which occur only 
in massive form. By the latter means Baumhauer* has succeeded 
in detecting irregular intergrowth of various substances in 
cloanthite and smaltite. The occurrence of thin lamelle of 
ittle Journonite3 crystals cover the cubic faces of galena 
from Pribram. Their long axes are either parallel to the com- 
bination edge between «Ox and O, or they are inclined to this 
at an angle of 45°. 
Crystallographic News.—The twinning law. of /epidolite + from 
Schiittenhofen, in Bohemia, is the same as that for the more 
common micas,—z.¢., the twinning plane is œP. The dispersion 
of the axes is very similar to that in the hemihedral crystals of 
the orthorhombic system. Intergrowths of muscovite and lepi- 
dolite take place parallel to the twinning position of micas of the 
Several brief communications on the crys- 
*Zeits. f. Kryst., xii. p. 18. 2 Ib., p. 40. 
C. Hintze, Ib., xi. kk. 4 R. Scharizer, ìb., xii. p. 1. 
[b., pp. 424 and 451. ; : 
f also Des Cloizeaux, Bull. d. 1. Soc. franç. de Min., 1886, p. 135. 
eits. f. Kryst., xii. p. 434- : i i 
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