q 
Anomalous crystals, 7.e., crystals whose optical properties — 
betray the existence of a different symmetry from that which 
their form would seem to indicate, are often traversed by rifts — 
and easily fly to pees: ; but this is not the case with mimetic 
crystals." 
Mention may conveniently be made here of another source of — 
change of symmetry closely resembling change produced by di- 
morphism, but of a very different nature :— 
When some of the ties holding the balls of a linked homo- 
geneous assemblage in their places are loosed, while others remain, 
it may happen that certain of the balls break away from their 
symmetrically situated positions among the rest which continue 
linked together as a continuous whole, and if the process takes 
place uniformly, 7.e., symmetrically, and the loose balls pass away, — 
a symmetrical skeleton framework will remain, having interstices 
or gaps symmetrically disposed.’ 
And we may conceive of such a framework being strained in 
the process, so that results follow which are anomalous with respect 
to the degree of symmetry of the unstrained framework. 
Or again, we may conceive that the removal of the loosed balls 
permits the parts of the framework, in obedience to the principle 
of closest-packing, to adjust themselves to a higher symmetry than 
that which they were able to attain while these balls were present. 
For comparison with these conclusions we may cite the be- 
haviour of zeolites when warmed. 
Thus, Rinne has shown that these water-holding minerals 
when heated and treated with oil to get rid of the turbidity which 
attends the loss of the water, manifest important changes of 
symmetry without disintegrating. 
- In some cases, e.g., natrolite, lowering of the symmetry accom- 
panied by twinning take place, the boundaries of the twinning 
640 Scientific Proceedings, Royal Dublin Society. 
a mM 
2 Pat 
1 Brauns, loc. cit., p. 2. These latter are, it is suggested, comparable to assem- 
blages of partivles which have grown by accretion after a dimorphous change to a 
lower symmetry has taken place, the added parts being therefore free from strain. 
Comp. pp. 632 and 641. 
2 The highly symmetrical skeleton assemblages thus arrived at are not to be con- 
founded with the grosser sponge-like structures subsequently described which are 
compared to crystalloids. (See p. 666.) 
