462 
IDDINGS. 
allel to the vertical axis, c, and sometimes parallel to the clino- 
axis, a. In the latter case they are generally twinned accord¬ 
ing to the Manebach law. In the former they exhibit, in 
some instances, the normal position of the optic axes and at 
others the abnormal position. 
The crystallization of orthoclase prisms of these two types 
may take place at the same time or may follow one another 
alternately. 
The essential characteristic of spherulitic growths is the 
crystallization of minerals from one or more points with a 
radiating or diverging arrangement. 
