I'KM'II KSKOl.A. 



M.-N. Kl. 



INTRODUCTION. 



1 he present writer recently proposed a classification of the crystalline 

 rocks in several mineral faciès ^ each of which comprises those rocks 

 whose mineral composition is dependent only on the chemical bulk com- 

 position, while a definite chemical composition always results in the same 

 set of minerals. \'ariations in the former are accompanied by parallel 

 regular variations in the latter. It is assumed that the rocks belonging 

 to a definite faciès have originated under similar temperature and pressure 

 conditions and have generally arrived at a state of equilibrium which ap- 

 pears to be independent of the mode of crystallization, either metamorphic 

 or magmatic. To each metamorphic facies may thus be paralleled an 

 igneous facies. 



The main facies-groups of rocks hitherto proposed are the following: 



Metamorphic facies Igneous facies Typical minerals 



Satiidinitc fades Dialnisc facies Sanidine, plagioclase, 



woUastonite, clino-ensta- 

 tite-diopside, cordierite, 



sillimanite, tridymite 

 and quartz. 



Orthoclase, plagioclase, 

 grossularite, woUastonite, 

 diopside, enstatite, cor- 

 dierite, andalusite (pseu- 

 dostable?), quartz. 

 Muscovite, albite, epidote, 

 calcite, dolomite, talc, 

 serpentine, chlorite. 

 Microcline, grossularite, 

 woUastonite, diopside, 

 hornblende-tremolite, 

 anthophyllite, almandite, 

 cordierite, sillimanite, 

 muscovite. 



Horiifels facies 



Gabbro facies 



Grceiiscliist facies 



A nip h i bol i te facies 



Helsiiikitc facies 



Honiblciidc-gabhro 

 facies 



' Pentti Eskola, The Mineral Facies of Rocks. Norsk Geologisk Tidsskrift, 1920. 



