EUDIALYTIC  SYENITE

 

Eudialyte is an attractive, rare, pinkish-red silicate mineral having a moderately complex chemistry.  Eudialyte is a sodium-calcium-cesium-iron-manganese-yttrium-zirconium hydroxychlorosilicate (Na4(Ca,Ce)2(Fe,Mn,Y)ZrSi8O22(OH,Cl)2).

 

The rocks shown below have a significant eudialyte component, along with sodic plagioclase feldspar (white) and arfvedsonite amphibole (black).  They are eudialytic peralkaline syenites (or metasyenites, as the rocks on the outcrop scale have a weakly developed, coarse-scale foliation).

 

Locality - apparently the “rare-earth occurrence” locality of Currie & Van Breemen (1996 - Canadian Mineralogist 34: 435-451) and Currie (1998 - Geological Survey of Canada Current Research 1998-C: 167-172), near the Kipawa River between Lake Sheffield and Lake Sairs, Villedieu Township, south-central Témiscamingué County, southwestern Quebec, southeastern Canada.

 

Geologic origin - published information indicates that the eudialyte is metasomatic in origin (= formed by the significant addition of chemicals to pre-existing rocks), and dates to about 994 million years (late Mesoproterozoic).  The host syenite rock is mid-Mesoproterozoic in age (~1.24 billion years).  It forms part of the Kipawa Syenite Complex in the Kipawa Syncline area of the Grenville Province, near the Grenville Province-Superior Province boundary.

 

Eudialytic metasyenite (6.8 cm across) from the Precambrian of Quebec, Canada.

 


 

Eudialytic metasyenite (4.9 cm across) from the Precambrian of Quebec, Canada.

 


 

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