VOLUME CHANGES IN METAMORPHISM 
WALDEMAR LINDGREN 
Massachusetts Institute of Technology, Cambridge 
Introduction.—It is the purpose of this paper to consider volume 
changes of rocks in relation to metamorphism. ‘This is a subject 
which has already received much attention by geologists and physi- 
cal chemists, but it seems to me that the former have not always 
appreciated the true conditions of metasomatism, while the latter 
have limited themselves largely to the consideration of transforma- 
tions In systems in open space. ‘The changes in the rigid rocks are 
subject to certain limitations to which I believe sufficient attention 
has not been directed. / 
Known changes of volume.—It is evident and well known that 
volume changes in rocks take place. The most efficient agencies 
are molecular forces: heating and cooling, fusion and solidification, 
molecular rearrangement (as when a mineral passes any inversion 
point). All of these may affect the volume of large or small masses 
of rocks. Injection of igneous material may increase the volume. 
Stretching of a geological body may result in cracks and fissures, 
increasing the bulk volume, and if these are filled by circulating 
solutions the actual volume will be greater than before. In the 
same way processes of filling may increase the actual volume of a 
porous rock. It is also well known that diminution of volume may 
take place in unconsolidated sediments under pressure, by closing 
of pores or other openings, and by incidental squeezing out of any 
fluid or gaseous phase which the rock may-contain. In such rocks 
lateral movements of plastic material may occur, though this 
would only effect a relative change of volume. Similar relative 
volume changes occur by recrystallization under conditions of rock 
flowage (as in case of marble or ice). 
Close to the surface where disintegrating agencies are at work . 
volume changes may take place. The pressure is slight and chem- 
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