SODALITE  &  LAZURITE

 

Sodalite & lazurite are two of several silicate minerals called feldspathoids.  Feldspathoids are chemically similar to the feldspars, but they have far less silica (SiO2) and end up enriched in sodium and/or potassium (typically).  These two sodalite-group feldspathoids are famous for their brilliant blue coloration.

 


 

Sodalite (field of view ~4.7 cm across) from a seam in Proterozoic-aged nepheline syenite at the Princess Sodalite Quarry in Bancroft, Ontario, Canada.

Sodalite is a sodium chloro-aluminosilicate (Na4(Al3Si3)O12Cl).  It is moderately hard (H=5.5 to 6).  Sodalite is uncommon, but can be found in some intrusive igneous rocks and some extrusive igneous rocks (lava flows).

 

 


 

Sodalite (7.5 cm across at its widest) from a pegmatitic nepheline syenite in the Poços de Caldas Alkaline Complex (mid-Campanian Stage, late Late Cretaceous, 76 to 78 million years); Poços de Caldas Plateau, Minas Gerais State, southeastern Brazil.

 


 

Photo gallery of sodalite

 



  

Lazurite (blue - the actual has a hint of purplish coloration not apparent in the photo) in pyritic marble (field of view ~2.5 cm across) from contact metamorphic marbles of the Sakhi Formation (Neoarchean) in the Hindu Kush Mountains of northeastern Afghanistan.  In this area, lazurite can be a rock-forming mineral.  Rocks dominated by lazurite are called lapis lazuli.

Lazurite is similar to sodalite, but is much rarer.  It has the moderately complex chemical formula  ((Na,Ca)8(AlSiO4)6(SO4,S,Cl)2).  Lazurite has a nonmetallic luster, is intensely blue in color, and has a hardness of about 5 to 5.5.  Lazurite tends to occur in contact metamorphic rocks.

 


 

Photo gallery of lazurite

 


 

Home page