84 l'KN'ni KSKOLA. M.-N. Kl. 



I hl li\ |)( isiliciii- occiii-.s in the ronii of equidimensional grains and 

 shows a (lisiincl. icd and i^iccn plfochroism. The optic character is nega- 

 tive and the axial angk- about '60 . 1 Icnce it should contain Tibout 

 25 niol. FeSiO.,. 



In die ,i;arn(tdH-aring zones the garnet occurs as rounded crystals 

 about 0.5 (111 in diameter, and their interstices are filled up with finely 

 granular hornblende. The garnet was separated and analyzed by the writer 

 with the lollowing result: 



Composition : (Fe.„MniMg,i.jCaij;.)3(Al.^Fe,st,. 



The sample was very free from an\' alien substances. We meet here 

 with a garnet in which ferrous oxide and magnesia are almost equal 

 in quantity. 



The hornblende is a green variety of medium intensity of the colours 

 sharing all the properties of common hornblende. Its mean index of re- 

 fraction was found to be fi = 1-655 ± 0.002. Towards the labradorite-rock 

 the hornblende protrudes as fairly euhedral prisms, showing well-developed 

 terminal faces. 



hi those zones free from garnet the hornblende frequently assumes a 

 somewhat coarser grain. Grains of dark green spinel surrounded by a 

 zone of plagioclase are seen in the hornblende mass. This plagioclase 

 seems, from its réfringence, to be at least as anorthitic as that in the 

 neighbouring rock. 



This garnet-bearing zone appears as a reaction zone between the 

 olivine and the labradorite, and in fact we could call it with Sederholm a 

 reaction-equation written in rock. Moreover, the petrologist sees here an 

 equation that he knows \er3' well, for F. Becke long ,ago wrote_ it as 

 an example of interaction between minerals during rock metamorphism, 

 whereby the product acquires a considerably smaller molecular volume 

 than the earlier combination : 



