PRINCIPLES UNDERLYING METAMORPHIC PROCESSES 613 
this we would consider only a simple equilibrium characteristic of 
relatively low temperatures, remembering always that the conclu- 
sions reached by this means are subject to considerable limitation; 
still such conclusions may be useful for purposes of classification, 
if for no others. 
i Corresponding Minerals in Products Obtained 
Main Components Stress Mineral | Katamorphic Rocks or in | on hae vt 
Eruptive Rocks use ae 
Ba fAlkali feldspar, mus-||beuctte, nephe- 
HO, ALO,, K.0, Si02...... Sericite i aanuee pare litic mineral, 
: glass 
H.O, Al.O;, K.0, MgO, FeO, : Olivine, spinel, 
1OhysinOo Sa Oo ceee Biotite Biotite leucite(?), 
edd glass 
Partly biotite, partly]. . cer 
HO, MgO, FeO, SiO. ..... Chlorite , olivine, spinel, {Sp a » olivine 
aisle AG Slee 
H.O, FeO, SiOz, ALOs...... @bloritoid) Me!) Coreiertee tag) Pe iat eae 
manite, spinel 
HO, FeO, Al.O;, SiO... ... Staurolite Sameas/chlontoids © if\...2 se ae aden 
Consist of plagiocla- 
ses in combination 
with pyroxenes, etc. : 
H.0, Fe.03, Al,O3;, CaO, SiO.) Epidote Epidote is also a cae sae 
primary constitu- ah Ses 
ent of some gran- 
ites } 
EO) ALO; Ca0,Si0;..... Zoisite See OBES i ede ee 
H,O, CaO, MgO, SiO....... Cee es Augite and olivine |.............. 
H,O, MgO, FeO, CaO, AIO; (In part) basaltic 
alkalies, SiO2..... oe Hornblendes |; hornblendes or te een 
pyroxenes 
Na.O, ALO,, SiO. {FeO | Glaucophane ? ? 
2U, £11203, "\MgOJ °° P £ : 
Anorthite, 
: ticellite 
2 JGarnet, plagioclase, aoe se 
CaO, MgO, FeO, A1,0;, SiO.| Garnet \. olivine, pyroxene Saupe eee 
nite’ 
5 Kyanite sSillimanite, anda- 
RO SIOS Ph ys Ks { Eeeiol Sie ee eee eee 
Influence of stress on reactions accompanied by the production 
of a vapor phase.—In considering the effects of stress it is absolutely 
essential to note that the influence of stress on reactions which 
are accompanied by the evolution of a gas or vapor is enormous. 
For instance, it is well established that continued grinding in a 
